The suspension stage of copper flash smelting was examined by roasting a high arsenic copper smelting feed mixture at 500-900°C for 0-20 s in nitrogen and air atmospheres.The enrichment of copper,lead,zinc,arseni...The suspension stage of copper flash smelting was examined by roasting a high arsenic copper smelting feed mixture at 500-900°C for 0-20 s in nitrogen and air atmospheres.The enrichment of copper,lead,zinc,arsenic,and sulfur in the quenched calcine was determined via chemical analyses.Pyrite and chalcopyrite were the main minerals in the feed mixture,and about 55 wt.%of arsenic was in tennantite.The stability of the feed and the formation of S_(2) and SO_(2)during roasting were surveyed by thermal analysis combined with mass spectrometry.Selected pure impurity sulfides were studied for reference purposes.Results indicated that arsenic was released more easily in inert atmosphere compared to air,in which oxidation products of sulfides captured the released gaseous arsenic.Kinetics analyses showed that the third-order chemical reaction and three-dimensional diffusion models were found as the most suitable mechanism functions of arsenic volatilization in inert and air atmospheres,respectively.展开更多
To recover the valuable elements in Bayan Obo tailings,Fe-Si bath smelting reduction was adopted to separate and enrich rare earth elements(REE),niobium and titanium from the REE-Nb-Ti-containing slag.The reduction re...To recover the valuable elements in Bayan Obo tailings,Fe-Si bath smelting reduction was adopted to separate and enrich rare earth elements(REE),niobium and titanium from the REE-Nb-Ti-containing slag.The reduction reaction process of the Fe-Si bath and the migration behavior of valuable elements in the solidification and crystallization process of silicothermic reduction tailings were investigated,and a treatment method for efficiently separating and enriching REE,Nb and Ti was explored.Thermodynamic analysis indicated that at 1600℃,with a 6 wt.%addition of Si as the reducing agent,the niobium oxide in the REE-Nb-Ti-containing slag could be selectively reduced to metallic Nb.In the Fe-Si bath reduction process,the Nb mass fraction in the metal phase increased with prolonged reaction time,peaking at 2.77%,while the Ti mass fraction consistently stayed below 0.12%.Lowering the w(CaO)/w(SiO_(2))enhanced the migration of Nb from slag to metal phase and reduced the Ti impurities.During solidification and crystallization,a significant quantity of perovskite precipitated from reduction tailings,with the REE dissolving into this perovskite.By adjusting the w(CaO)/w(SiO_(2))in tailings to 1.2-1.9 and maintaining a temperature of 1100℃for 4 h,the perovskite area fraction in the final slag could exceed 37%.Finally,a method was proposed to separate and enrich valuable elements in REE-Nb-Ti-containing slags via Fe-Si bath smelting reduction and crystallization control.展开更多
Antimony smelting activities damage the soil and vegetation surroundings while generating economic value.However,no standardizedmethods are available to diagnose the extent of soil degradation at antimony smelting sit...Antimony smelting activities damage the soil and vegetation surroundings while generating economic value.However,no standardizedmethods are available to diagnose the extent of soil degradation at antimony smelting sites.This study developed a standardized framework for assessing soil quality by consideringmicrobial-induced resilience and heavymetal contamination at Xikuangshan antimony smelting site.The soil resilience index(SRI)and soil contamination index(SCI)were calculated byMinimum Data Set and geo-accumulation model,respectively.After standardized by a multi-criteria quantitative procedure of modified Nemerow’s pollution index(NPI),the integrated assessment of soil quality index(SQI),which is the minimumof SRINPI and SCINPI,was achieved.The results showed that Sb and As were the prominent metal(loid)pollutants,and significant correlations between SQI and SRI indicated that the poor soil quality was mainly caused by the low level of soil resilience.The primary limiting factors of SRI were Fungi in high andmiddle contaminated areas,and Skermanella in low contaminated area,suggesting that the weak soil resilience was caused by low specific microbial abundances.Microbial regulation and phytoremediation are greatly required to improve the soil quality at antimony smelting sites from the perspectives of pollution control and resilience improvement.This study improves our understanding of ecological effects of antimony smelting sites and provides a theoretical basis for ecological restoration and sustainable development of mining areas.展开更多
Copper smelting is the main source of arsenic pollution in the environment,and China is the largest country for copper smelting.Taking 2022 as an example,this study analyzes the distribution and fate of arsenic across...Copper smelting is the main source of arsenic pollution in the environment,and China is the largest country for copper smelting.Taking 2022 as an example,this study analyzes the distribution and fate of arsenic across the copper mining,beneficiation,and smelting processes using a life-cycle approach,providing important insights for arsenic pollution prevention and the resource utilization of arsenic-bearing solid waste.The results show that the amount of As in waste rock,tailing and concentrate are 53483 t,86632 t,76162 t,respectively.After smelting treatment,the amount of arsenic in different types of solid waste,wastewater,waste gas and products are 76128 t,1 t,31 t and 2 t,respectively,and the proportion in arsenic sulfide slag is the highest(55%).The amount of emission to the environment is 32 t,accounting for only 0.04%of total amount.In the future,key considerations are to improve the resource utilization rate of arsenic-containing solid waste(tailing,smelting slag),especially arsenic sulfide slag,and to digest its environmental risk.展开更多
Rare earth elements(REEs)play a crucial role in many technologies from daily appliances in cell phones to more advanced wind turbines and electric cars.Permanent magnets account for a quarter of total global REEs prod...Rare earth elements(REEs)play a crucial role in many technologies from daily appliances in cell phones to more advanced wind turbines and electric cars.Permanent magnets account for a quarter of total global REEs production and have high recycling value.In this study,smelting process was used to selectively oxidize REEs in the permanent magnets by adding Fe_(2)O_(3).This separates REEs into a slag phase from an iron-rich metallic phase.B_(2)O_(3) was also added to the system as a flux to lower the slag melting temperature.This minimizes REEs loss to the metallic phase and allows a more efficient phase separation.The effect of flux and oxidizing agent addition was investigated on both regular and cerium-rich NdFeB(NdCeFeB)magnets.At 1350℃and for 1 h,the slag phase was successfully separated from the metallic phase with the addition of 0.8 stoichiometric amount of Fe_(2)O_(3) and 40 wt%of B_(2)O_(3).Scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDX)analysis reveals that REEs in the magnet do not migrate to the metal phase while the REE-rich slag phase contains almost no iron.After the selective removal of iron into the metallic phase,REEs are recovered from the slag phase through an acid leaching process allowing>99%of REEs recovery.Boron in the magnet can also be recovered as useful boric acid by evaporation and crystallisation technique.The proposed process in this study is reagent and energy-efficient with almost complete valorisation of both NdCeFeB and NdFeB magnets.展开更多
Non-ferrous metal smelting poses significant risks to public health.Specifically,the copper smelting process releases arsenic,a semi-volatile metalloid,which poses an emerging exposure risk to both workers and nearby ...Non-ferrous metal smelting poses significant risks to public health.Specifically,the copper smelting process releases arsenic,a semi-volatile metalloid,which poses an emerging exposure risk to both workers and nearby residents.To comprehensively understand the internal exposure risks of metal(loid)s from copper smelting,we explored eighteen metal(loid)s and arsenic metabolites in the urine of both occupational and non-occupational populations using inductively coupled plasma mass spectrometry with high-performance liquid chromatography and compared their health risks.Results showed that zinc and copper(485.38 and 14.00μg/L),and arsenic,lead,cadmium,vanadium,tin and antimony(46.80,6.82,2.17,0.40,0.44 and 0.23μg/L,respectively)in workers(n=179)were significantly higher compared to controls(n=168),while Zinc,tin and antimony(412.10,0.51 and 0.15μg/L,respectively)of residents were significantly higher than controls.Additionally,workers had a higher monomethyl arsenic percentage(MMA%),showing lower arsenic methylation capacity.Source appointment analysis identified arsenic,lead,cadmium,antimony,tin and thallium as co-exposure metal(loid)s from copper smelting,positively relating to the age of workers.The hazard index(HI)of workers exceeded 1.0,while residents and control were approximately at 1.0.Besides,all three populations had accumulated cancer risks exceeding 1.0×10^(-4),and arsenite(AsIII)was the main contributor to the variation of workers and residents.Furthermore,residents living closer to the smelting plant had higher health risks.This study reveals arsenic exposure metabolites and multiple metals as emerging contaminants for copper smelting exposure populations,providing valuable insights for pollution control in non-ferrous metal smelting.展开更多
The properties of direct reduced iron(DRI)smelting slag are important in the DRI melting process for molten iron production to ensure the slag-iron separation and quality of molten iron.The influence of binary basicit...The properties of direct reduced iron(DRI)smelting slag are important in the DRI melting process for molten iron production to ensure the slag-iron separation and quality of molten iron.The influence of binary basicity on the viscosity and sulfide capacity of CaO-SiO_(2)-MgO-Al_(2)O_(3)-FeO slag was investigated by the high-temperature experiments,structural analysis and thermodynamic calculation.The viscosity of the slag decreased rapidly with an increase in basicity from 0.4 to 0.8,and this trend became slow as the basicity further increased to 1.2.For the acidic slag with basicity of 0.4 and 0.6,the viscosity at 1500℃ was higher than 0.6 Pa s,which was harmful for the fluidity of slag melt.The slags with basicity of 0.8,1.0 and 1.2 at 1500℃ showed the low viscosity of less than 0.6 Pa s.For the basic slag with basicity of 1.0 and 1.2,the rapid precipitation of melilite led to the abrupt increase behavior of the viscosity,and the acidic slag showed the gentle temperature-viscosity curves.The Raman analysis revealed that the conversion from Q^(3) to Q^(2),Q^(1) and Q^(0) mainly occurred with the basicity increasing from 0.4 to 0.8,and the conversion from Q^(2) to Q^(1) and Q^(0) was dominant with further increase in basicity to 1.2,decreasing the degree of polymerization.The sulfide capacity was improved with the increasing basicity due to the increase in O^(2-)ions,and CaS could be formed dominantly for S^(2-)stabilization in present slag.The sulfur partition ratio was derived from sulfide capacity,and the values of sulfur partition ratio at basicity of 0.4 and 0.6 were much smaller than those at basicity of 0.8,1.0 and 1.2,indicating a weak desulfurization ability of the slag with a low basicity.展开更多
Stainless steel,known for its exceptional properties and diverse applications,conventionally requires a multistage process that generates considerable CO_(2) emissions by using fossil-based carbon reductants.This stud...Stainless steel,known for its exceptional properties and diverse applications,conventionally requires a multistage process that generates considerable CO_(2) emissions by using fossil-based carbon reductants.This study investigated hydrogen plasma smelting reduction as a novel,sustainable,and efficient method for producing stainless steel directly from lateritic nickel and chromite ores.The research aimed to examine the effect of ore proportion on AISI 300 series stainless steel production and assess the reduction process over time through thermochemical calculations and experimental studies.Results showed that increasing the proportion of chromite ore in the feed raises Cr content and reduces Ni content in metals while increasing Cr_(2)O_(3) and Al_(2)O_(3) content in oxides.A briquette comprising 30wt%chromite ore and 70wt%calcined nickel ore yields better results for AISI 300 stainless steel,with Fe,Cr,Ni,and Si content of 62.95wt%,19.37wt%,11.83wt%,and 0.72wt%,respectively,after 180 s of hydrogen plasma exposure.Nearly all NiO compounds are converted into Ni after 60 s of smelting reduction,whereas FeO compounds are almost fully converted into Fe after 120 s of smelting reduction.AISI 300 series stainless steel is successfully produced after 120 s of reduction,achieving Fe,Cr,Ni,and Si content of 64.36wt%,21.92wt%,10.08wt%,and 0.61wt%,respectively.Process optimization remains promising because the Cr_(2)O_(3) content in the slag is still relatively high at 15.52wt%.This ultrafast and direct production method holds considerable potential to transform stainless steel production by reducing environmental impact and enhancing process efficiency.Specifically,the method eliminates the use of an argon oxygen decarburization converter and vacuum oxygen decarburization in stainless steelmaking.展开更多
The semi-molten smelting process of a mixture of saprolitic and limonitic laterite ores was systematically investigated and the effect of slag basicity was deeply analyzed.The results indicate that the slag system can...The semi-molten smelting process of a mixture of saprolitic and limonitic laterite ores was systematically investigated and the effect of slag basicity was deeply analyzed.The results indicate that the slag system can be located in the liquidus region of low melting-point diopside(CaMgSi_(2)O_(6))when slag basicity is kept at 0.3 and limonitic laterite mass fraction is not less than 10%.When the reduction temperature,C/O mass ratio,limonitic laterite mass fraction and slag basicity are kept at the optimum values of 1300℃,0.86,20%and 0.3,respectively,ferronickel products with grades 6.42%Ni and 86.99%Fe are prepared.The recovery rates of Ni and Fe reach 88.60%and 72.25%,respectively.展开更多
Under complicated field conditions,such as the coupled effects of freeze-thaw cycles(FTs)and acidification,the leaching behavior of potentially toxic element(PTEs)from indigenous Zn smelting slags(ZSS)was intricately ...Under complicated field conditions,such as the coupled effects of freeze-thaw cycles(FTs)and acidification,the leaching behavior of potentially toxic element(PTEs)from indigenous Zn smelting slags(ZSS)was intricately connected to the mineralogy(e.g.,the composition,assemblage,microstructure of mineral particles).In this study,FTs tests were carried out to explore the interactions between PTEs release and ZSSmineralogy.Subsequently,advanced characterization techniqueswere adopted to quantify the mineralogy andmicrostructure of ZSS.The results indicated that ZSS were mainly composed of silicate minerals(e.g.,quartz,biotite and chlorite)and secondary Fe(III)oxyhydroxides(e.g.,magnetite and limonite),accounting for 67.48% and 24.23%,respectively.The occurrence mode analysis revealed that 81.95%of As,21.31%of Pb and 7.77% of Zn were hosted in limonite.About 37.89%,59.34% and 34.50% of Cd,Pb and Zn were associated with carbonate bound fractions.Under FTs interacting with different pH conditions,the leaching concentrations of As,Cd,Cu,Pb and Zn did not significantly increase with the increase in FTs and pH.The microstructure damage of mineral particles in ZSS with the higher porosity was caused by both FTs and proton corrosion.More importantly,the geochemical modeling results suggested that the precipitation of hematite and magnetite,as well as the dissolution of arsenolite,might have little impacts on PTEs release under FTs and FTs with acidification.This work would provide a deeper understanding of PTEs release from smelting waste slags under complex physicochemical interactions.展开更多
A major problem facing the magnesium melting process is to address the oxidative combustion of magnesium.At present,there are still some problems in the method used to protect magnesium smelting.For example,the reacti...A major problem facing the magnesium melting process is to address the oxidative combustion of magnesium.At present,there are still some problems in the method used to protect magnesium smelting.For example,the reaction of covering flux with magnesium melt is likely to produce a large number of toxic and harmful gasses(Cl_(2) and HCl),the cost of such reaction is high,and there is a lack of clarity on the protection mechanism of CO_(2) acting as the protective gas of magnesium melt.Therefore,a new process is proposed in this paper to isolate the air on the surface of magnesium melt using MgO-C-Mg film.Based on the thermodynamic theory of MgO-C-Mg film formation during crude magnesium smelting,an investigation is conducted into the effect of different experimental conditions on the protective effect of magnesium.Not only is the protective mechanism of MgO-C-Mg film revealed,it is also verified that the MgO-C-Mg film can produce a more pronounced protective effect at suitable temperature.According to thermodynamic analysis,magnesium melt reacts with CO_(2) to form magnesium oxide and C.CO_(2) consumes C when the experimental temperature exceeds 700℃.This is contrary to the purpose of the experiment as it should be maintained at about 700℃.The experimental results show that an obvious protective effect can be produced on the magnesium melt by the MgO-C-Mg film generated under the following conditions of 90%CO_(2)-10%Ar,smelting temperature of 700℃,holding time of 60 min,and stirring time of 20 min.展开更多
The melting and separation behavior of vanadium-titanium magnetite pellets directed at an efficient extraction of vanadium and titanium was systematically investigated.Applying FactSage simulations and experiments,the...The melting and separation behavior of vanadium-titanium magnetite pellets directed at an efficient extraction of vanadium and titanium was systematically investigated.Applying FactSage simulations and experiments,the smelting separation of three pre-reduced pellets from different regions was analyzed.The simulations demonstrate that FeTi2O5 is converted to TiC at low temperatures,necessitating suppression of this step.Experiments under optimized conditions(1590-1690°C,20-25 min,2%coke,basicity 0.4-0.6,and 3.0%-6.0%MgO)yield iron grade of 92.35%-95.06%,titanium grade of 34.37%-39.89%,and vanadium grade of 0.56%-1.52%,with recoveries of 99.52%-99.60%,94.08%-98.96%,and 92.63%-94.38%for iron,titanium and vanadium,respectively.The titanium in the slag,primarily in the form of anosovite,is suitable for sulfuric acid-based titanium white production.An increase in basicity,MgO content,and pellet metallization serves to improve vanadium recovery in melted iron but lowers the titanium grade in the slag.The overall process effectively utilizes vanadium and titanium resources under optimized conditions.展开更多
A process for treating cyanide tailings was proposed.The process essentially implicates reduction smelting which involves volatilizing silver,lead,and zinc in the cyanide tailings at high temperatures.Meanwhile,gold a...A process for treating cyanide tailings was proposed.The process essentially implicates reduction smelting which involves volatilizing silver,lead,and zinc in the cyanide tailings at high temperatures.Meanwhile,gold and copper combine with the reduced iron to form a metal phase,allowing for the simultaneous recovery of polymetallic elements.The experimental results indicate that the process works optimally with a coke powder of 7.5 wt.%,an alkalinity of 1.0,a melting temperature of 1450℃,and a melting time of 60 min.Under these conditions,more than 99% of gold,77% of copper and 94% of iron are incorporated into pig iron.In the meantime,the volatilization rate of silver exceeds 90%,while lead and zinc are essentially completely volatilized.The primary component of the by-product smelting slag is akermanite,which exhibits lower leaching toxicity than the national standard and belongs to general solid waste.Additionally,taking the trapping process of iron to copper as a case study,the mechanism of iron trapping is methodically examined and divided into three processes:smelting reduction,migration capture,and condensation deposition.展开更多
NA novel smelting reduction process based on FeO-SiO2-Al2O3 slag system for spent lithium ion batteries with Al cans was developed, while using copper slag as the only slag former. The feasibility of the process and t...NA novel smelting reduction process based on FeO-SiO2-Al2O3 slag system for spent lithium ion batteries with Al cans was developed, while using copper slag as the only slag former. The feasibility of the process and the mechanism of copper loss in slag were investigated. 98.83% Co, 98.39% Ni and 93.57% Cu were recovered under the optimum conditions of slag former/battery mass ratio of 4.0：1, smelting temperature of 1723 K, and smelting mass ratio of time of 30 min. The FeO-SiO2-Al2O3 slag system for the smelting process is appropriate under the conditions of m（FeO）：m（SiO2）=0.58：1？1.03：1, and 17.19%？21.52% Al2O3 content. The obtained alloy was mainly composed of Fe-Co-Cu-Ni solid solution including small amounts of matte. The obtained slag mainly consisted of fayalite and hercynite. Meanwhile, the mechanism of copper loss is the mechanical entrainment from strip-like fayalite particles in the main form of copper sulfide and metallic copper.展开更多
A field investigation was performed to study the content, speciation and mobility of vanadium, as well as microbial response in soil from a stone coal smelting district in Hunan province of China. The results showed t...A field investigation was performed to study the content, speciation and mobility of vanadium, as well as microbial response in soil from a stone coal smelting district in Hunan province of China. The results showed that the contents of soil V ranged from 168 to 1538 mg/kg, which exceeded the maximum permissible value of Canadian soil quality for V. The mean soil V content from wasteland area reached 1421 mg/kg, and those from the areas related with slag heap, ore pile and smelting center were 380, 260 and 225 mg/kg, respectively. Based on the results of the modified BCR sequential extraction procedure, V contents in the mobile fractions varied from 19.2 to 637 mg/kg accounting for 7.4%-42.3% of total V, and those of V(+5) species were between 21.9 and 534.0 mg/kg. Soil enzyme activity and microbial basal respiration were adversely affected by high level of soil V. More attention should be paid to soil V pollution and potential hazardous surrounding the stone coal smelting district.展开更多
The reduction smelting process for cobalt recovery from converter slag of the Chambishi Copper Smelter in Zambia was studied. The effects of reducing agent dosage, smelting temperature and time and the addition of sla...The reduction smelting process for cobalt recovery from converter slag of the Chambishi Copper Smelter in Zambia was studied. The effects of reducing agent dosage, smelting temperature and time and the addition of slag modifiers （CaO and TiO2） were investigated. In addition, the depleted slag and cobalt-bearing alloy were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Under the determined conditions, 94.02% Co, 95.76% Cu and less than 18% Fe in the converter slag were recovered. It was found that the main phases of depleted slag were fayalite and hercynite; and the cobalt-bearing alloy mainly contained metallic copper, Fe-Co-Cu alloys and a small amount of sulfide.展开更多
According to the innate characteristic of four types of furnace, the copper flash continuous smelting （CFCS） furnace can be considered a synthetic reactor of two relatively independent processes： flash matte smelti...According to the innate characteristic of four types of furnace, the copper flash continuous smelting （CFCS） furnace can be considered a synthetic reactor of two relatively independent processes： flash matte smelting process （FMSP） and copper continuous converting process （CCCP）. Then, the CFCS thermodynamic model was proposed by establishing the multi-phase equilibrium model of FMSP and the local-equilibrium model of CCCP, respectively, and by combining them through the smelting intermediates. Subsequently, the influences of the furnace structures were investigated using the model on the formation of blister copper, the Fe3O4 behavior, the copper loss in slag and the copper recovery rate. The results show that the type D furnace, with double flues and a slag partition wall, is an ideal CFCS reactor compared with the other three types furnaces. For CFCS, it is effective to design a partition wall in the furnace to make FMSP and CCCP perform in two relatively independent zones, respectively, and to make smelting gas and converting gas discharge from respective flues.展开更多
The effects of moderately thermophilic bacteria on the extraction of metals from zinc smelting slag and electrochemical characteristics of zinc smelting slag carbon paste electrode in bioleaching process were studied....The effects of moderately thermophilic bacteria on the extraction of metals from zinc smelting slag and electrochemical characteristics of zinc smelting slag carbon paste electrode in bioleaching process were studied. The results show that the extraction rates of Fe, Cu and Zn from the slag reach 86.7%, 90.3% and 66.7% after adsorbed bacteria sterilize, while those with adsorbed bacteria are 91.9%, 96.0% and 84.5% in conditions of pulp density 2%, pH 1.0, temperature 65 °C and stirring rate 120 r/min, respectively. Some stretching peaks of functional groups from bacterial secretes on the bioleached residue surface, such as 1007 cm-1 and 1193 cm-1, turn up through FI-IR analysis and indirectly reveal the presence of the adsorbed bacteria on the slag particles surface. Besides, the corrosion of zinc smelting slag is enhanced by bacteria according to the characteristics of cyclic voltametry and Tafel curves in bioleaching system.展开更多
A new process for utilization of hazardous lead-bearing wastes and iron-rich wastes by reducing-matting smelting has been developed.The slag（SG） and the iron-rich matte（IRM） are the main by-products from reducing-...A new process for utilization of hazardous lead-bearing wastes and iron-rich wastes by reducing-matting smelting has been developed.The slag（SG） and the iron-rich matte（IRM） are the main by-products from reducing-matting smelting of lead-bearing wastes and iron-rich wastes.The environmental risk of heavy metals（Cd,Zn,Pb and As） in the main by-products versus the charging material for reducing-matting smelting（CM） has been systematically assessed using leaching toxicity test,the three-stage sequential extraction procedure of European Community Bureau of Reference（BCR） and Hakanson Potential Ecological Risk Index Method（PERI）.The results demonstrate that the ecological risk level of heavy metals for SG and IRM is significantly reduced after the reducing-matting smelting process compared with that for CM.展开更多
A mathematical model has been presented to study the combustion of a single copper concentrate particle with high moisture content. By using the presented model, the effect of particle moisture content on particle tem...A mathematical model has been presented to study the combustion of a single copper concentrate particle with high moisture content. By using the presented model, the effect of particle moisture content on particle temperature, sulfur oxidation, and combustion heat generation has been evaluated. The mineralogical composition of the commonly used concentrate at Khatoonabad flash smelting furnace has been used in this study. It was found that the particle moisture content is removed in the sub-second time range and thus the moisture has marginal impact on the variation of particle temperature and on the reaction rate when the gas temperature is assumed to be constant in the reaction shaft. When a concentrate with high moisture content is charged, the particle size enlargement due to the agglomeration of concentrate particles causes an abrupt fall in the particle reaction rate.展开更多
基金support from the Research Foundation for Doctor of Nanyang Institute of Technology,China(No.NGBJ-2022-27)the National Key Research and Development Program of China(No.2023YFC3904002)+3 种基金the National Natural Science Foundation of China(Nos.52064038,52364056)the Science and Technology Research Project of Henan Province,China(No.252102320113)the Key Scientific Research Project Plan of Colleges and Universities in Henan Province,China(No.25B610009)Jiangxi Provincial Natural Science Foundation,China(Nos.20232BCJ22049,20232ACB214009).
文摘The suspension stage of copper flash smelting was examined by roasting a high arsenic copper smelting feed mixture at 500-900°C for 0-20 s in nitrogen and air atmospheres.The enrichment of copper,lead,zinc,arsenic,and sulfur in the quenched calcine was determined via chemical analyses.Pyrite and chalcopyrite were the main minerals in the feed mixture,and about 55 wt.%of arsenic was in tennantite.The stability of the feed and the formation of S_(2) and SO_(2)during roasting were surveyed by thermal analysis combined with mass spectrometry.Selected pure impurity sulfides were studied for reference purposes.Results indicated that arsenic was released more easily in inert atmosphere compared to air,in which oxidation products of sulfides captured the released gaseous arsenic.Kinetics analyses showed that the third-order chemical reaction and three-dimensional diffusion models were found as the most suitable mechanism functions of arsenic volatilization in inert and air atmospheres,respectively.
基金supported by the National Key R&D Program of China(No.2021YFC2901200)National Natural Science Foundation of China(Nos.52174383 and 52374412)Liaoning Provincial Natural Science Foundation of China(No.2022-YQ-09).
文摘To recover the valuable elements in Bayan Obo tailings,Fe-Si bath smelting reduction was adopted to separate and enrich rare earth elements(REE),niobium and titanium from the REE-Nb-Ti-containing slag.The reduction reaction process of the Fe-Si bath and the migration behavior of valuable elements in the solidification and crystallization process of silicothermic reduction tailings were investigated,and a treatment method for efficiently separating and enriching REE,Nb and Ti was explored.Thermodynamic analysis indicated that at 1600℃,with a 6 wt.%addition of Si as the reducing agent,the niobium oxide in the REE-Nb-Ti-containing slag could be selectively reduced to metallic Nb.In the Fe-Si bath reduction process,the Nb mass fraction in the metal phase increased with prolonged reaction time,peaking at 2.77%,while the Ti mass fraction consistently stayed below 0.12%.Lowering the w(CaO)/w(SiO_(2))enhanced the migration of Nb from slag to metal phase and reduced the Ti impurities.During solidification and crystallization,a significant quantity of perovskite precipitated from reduction tailings,with the REE dissolving into this perovskite.By adjusting the w(CaO)/w(SiO_(2))in tailings to 1.2-1.9 and maintaining a temperature of 1100℃for 4 h,the perovskite area fraction in the final slag could exceed 37%.Finally,a method was proposed to separate and enrich valuable elements in REE-Nb-Ti-containing slags via Fe-Si bath smelting reduction and crystallization control.
基金supported by the National Key Research and Development Program of China (No.2019YFC1803604)the National Natural Science Foundation of China (Nos.42007306 and 42277193).
文摘Antimony smelting activities damage the soil and vegetation surroundings while generating economic value.However,no standardizedmethods are available to diagnose the extent of soil degradation at antimony smelting sites.This study developed a standardized framework for assessing soil quality by consideringmicrobial-induced resilience and heavymetal contamination at Xikuangshan antimony smelting site.The soil resilience index(SRI)and soil contamination index(SCI)were calculated byMinimum Data Set and geo-accumulation model,respectively.After standardized by a multi-criteria quantitative procedure of modified Nemerow’s pollution index(NPI),the integrated assessment of soil quality index(SQI),which is the minimumof SRINPI and SCINPI,was achieved.The results showed that Sb and As were the prominent metal(loid)pollutants,and significant correlations between SQI and SRI indicated that the poor soil quality was mainly caused by the low level of soil resilience.The primary limiting factors of SRI were Fungi in high andmiddle contaminated areas,and Skermanella in low contaminated area,suggesting that the weak soil resilience was caused by low specific microbial abundances.Microbial regulation and phytoremediation are greatly required to improve the soil quality at antimony smelting sites from the perspectives of pollution control and resilience improvement.This study improves our understanding of ecological effects of antimony smelting sites and provides a theoretical basis for ecological restoration and sustainable development of mining areas.
文摘Copper smelting is the main source of arsenic pollution in the environment,and China is the largest country for copper smelting.Taking 2022 as an example,this study analyzes the distribution and fate of arsenic across the copper mining,beneficiation,and smelting processes using a life-cycle approach,providing important insights for arsenic pollution prevention and the resource utilization of arsenic-bearing solid waste.The results show that the amount of As in waste rock,tailing and concentrate are 53483 t,86632 t,76162 t,respectively.After smelting treatment,the amount of arsenic in different types of solid waste,wastewater,waste gas and products are 76128 t,1 t,31 t and 2 t,respectively,and the proportion in arsenic sulfide slag is the highest(55%).The amount of emission to the environment is 32 t,accounting for only 0.04%of total amount.In the future,key considerations are to improve the resource utilization rate of arsenic-containing solid waste(tailing,smelting slag),especially arsenic sulfide slag,and to digest its environmental risk.
基金Project supported by the Science and Engineering Research Board of India(SRG/2020/002096)。
文摘Rare earth elements(REEs)play a crucial role in many technologies from daily appliances in cell phones to more advanced wind turbines and electric cars.Permanent magnets account for a quarter of total global REEs production and have high recycling value.In this study,smelting process was used to selectively oxidize REEs in the permanent magnets by adding Fe_(2)O_(3).This separates REEs into a slag phase from an iron-rich metallic phase.B_(2)O_(3) was also added to the system as a flux to lower the slag melting temperature.This minimizes REEs loss to the metallic phase and allows a more efficient phase separation.The effect of flux and oxidizing agent addition was investigated on both regular and cerium-rich NdFeB(NdCeFeB)magnets.At 1350℃and for 1 h,the slag phase was successfully separated from the metallic phase with the addition of 0.8 stoichiometric amount of Fe_(2)O_(3) and 40 wt%of B_(2)O_(3).Scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDX)analysis reveals that REEs in the magnet do not migrate to the metal phase while the REE-rich slag phase contains almost no iron.After the selective removal of iron into the metallic phase,REEs are recovered from the slag phase through an acid leaching process allowing>99%of REEs recovery.Boron in the magnet can also be recovered as useful boric acid by evaporation and crystallisation technique.The proposed process in this study is reagent and energy-efficient with almost complete valorisation of both NdCeFeB and NdFeB magnets.
基金supported by the National Key Research and Development Project(Nos.2019YFC1804503 and 2019YFC1804504)the National Natural Science Foundation of China(No.41731279)the Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program(No.2017BT01Z032).
文摘Non-ferrous metal smelting poses significant risks to public health.Specifically,the copper smelting process releases arsenic,a semi-volatile metalloid,which poses an emerging exposure risk to both workers and nearby residents.To comprehensively understand the internal exposure risks of metal(loid)s from copper smelting,we explored eighteen metal(loid)s and arsenic metabolites in the urine of both occupational and non-occupational populations using inductively coupled plasma mass spectrometry with high-performance liquid chromatography and compared their health risks.Results showed that zinc and copper(485.38 and 14.00μg/L),and arsenic,lead,cadmium,vanadium,tin and antimony(46.80,6.82,2.17,0.40,0.44 and 0.23μg/L,respectively)in workers(n=179)were significantly higher compared to controls(n=168),while Zinc,tin and antimony(412.10,0.51 and 0.15μg/L,respectively)of residents were significantly higher than controls.Additionally,workers had a higher monomethyl arsenic percentage(MMA%),showing lower arsenic methylation capacity.Source appointment analysis identified arsenic,lead,cadmium,antimony,tin and thallium as co-exposure metal(loid)s from copper smelting,positively relating to the age of workers.The hazard index(HI)of workers exceeded 1.0,while residents and control were approximately at 1.0.Besides,all three populations had accumulated cancer risks exceeding 1.0×10^(-4),and arsenite(AsIII)was the main contributor to the variation of workers and residents.Furthermore,residents living closer to the smelting plant had higher health risks.This study reveals arsenic exposure metabolites and multiple metals as emerging contaminants for copper smelting exposure populations,providing valuable insights for pollution control in non-ferrous metal smelting.
基金the financial support from China Postdoctoral Science Foundation(2024M750177)National Natural Science Foundation of China(52474345)and Science and Technology Major Project of WuHan(2023020302020572).
文摘The properties of direct reduced iron(DRI)smelting slag are important in the DRI melting process for molten iron production to ensure the slag-iron separation and quality of molten iron.The influence of binary basicity on the viscosity and sulfide capacity of CaO-SiO_(2)-MgO-Al_(2)O_(3)-FeO slag was investigated by the high-temperature experiments,structural analysis and thermodynamic calculation.The viscosity of the slag decreased rapidly with an increase in basicity from 0.4 to 0.8,and this trend became slow as the basicity further increased to 1.2.For the acidic slag with basicity of 0.4 and 0.6,the viscosity at 1500℃ was higher than 0.6 Pa s,which was harmful for the fluidity of slag melt.The slags with basicity of 0.8,1.0 and 1.2 at 1500℃ showed the low viscosity of less than 0.6 Pa s.For the basic slag with basicity of 1.0 and 1.2,the rapid precipitation of melilite led to the abrupt increase behavior of the viscosity,and the acidic slag showed the gentle temperature-viscosity curves.The Raman analysis revealed that the conversion from Q^(3) to Q^(2),Q^(1) and Q^(0) mainly occurred with the basicity increasing from 0.4 to 0.8,and the conversion from Q^(2) to Q^(1) and Q^(0) was dominant with further increase in basicity to 1.2,decreasing the degree of polymerization.The sulfide capacity was improved with the increasing basicity due to the increase in O^(2-)ions,and CaS could be formed dominantly for S^(2-)stabilization in present slag.The sulfur partition ratio was derived from sulfide capacity,and the values of sulfur partition ratio at basicity of 0.4 and 0.6 were much smaller than those at basicity of 0.8,1.0 and 1.2,indicating a weak desulfurization ability of the slag with a low basicity.
文摘Stainless steel,known for its exceptional properties and diverse applications,conventionally requires a multistage process that generates considerable CO_(2) emissions by using fossil-based carbon reductants.This study investigated hydrogen plasma smelting reduction as a novel,sustainable,and efficient method for producing stainless steel directly from lateritic nickel and chromite ores.The research aimed to examine the effect of ore proportion on AISI 300 series stainless steel production and assess the reduction process over time through thermochemical calculations and experimental studies.Results showed that increasing the proportion of chromite ore in the feed raises Cr content and reduces Ni content in metals while increasing Cr_(2)O_(3) and Al_(2)O_(3) content in oxides.A briquette comprising 30wt%chromite ore and 70wt%calcined nickel ore yields better results for AISI 300 stainless steel,with Fe,Cr,Ni,and Si content of 62.95wt%,19.37wt%,11.83wt%,and 0.72wt%,respectively,after 180 s of hydrogen plasma exposure.Nearly all NiO compounds are converted into Ni after 60 s of smelting reduction,whereas FeO compounds are almost fully converted into Fe after 120 s of smelting reduction.AISI 300 series stainless steel is successfully produced after 120 s of reduction,achieving Fe,Cr,Ni,and Si content of 64.36wt%,21.92wt%,10.08wt%,and 0.61wt%,respectively.Process optimization remains promising because the Cr_(2)O_(3) content in the slag is still relatively high at 15.52wt%.This ultrafast and direct production method holds considerable potential to transform stainless steel production by reducing environmental impact and enhancing process efficiency.Specifically,the method eliminates the use of an argon oxygen decarburization converter and vacuum oxygen decarburization in stainless steelmaking.
基金supports from the National Key R&D Program of China(No.2022YFC3901404)the Natural Science Foundation of Chongqing,China(No.CSTB2023NSCQ-BHX0166)the Fundamental Research Funds for the Central Universities,China(No.2023CDJXY-016)are sincerely acknowledged.
文摘The semi-molten smelting process of a mixture of saprolitic and limonitic laterite ores was systematically investigated and the effect of slag basicity was deeply analyzed.The results indicate that the slag system can be located in the liquidus region of low melting-point diopside(CaMgSi_(2)O_(6))when slag basicity is kept at 0.3 and limonitic laterite mass fraction is not less than 10%.When the reduction temperature,C/O mass ratio,limonitic laterite mass fraction and slag basicity are kept at the optimum values of 1300℃,0.86,20%and 0.3,respectively,ferronickel products with grades 6.42%Ni and 86.99%Fe are prepared.The recovery rates of Ni and Fe reach 88.60%and 72.25%,respectively.
基金supported by the National Key Research and Development Program of China(Nos.2023YFC3707704 and 2019YFC1805205)the Research Initiation Fund and the 16th Batch of Sailing Plan Project of China University of Mining and Technology(Nos.102524004 and 102524096)the key scientific research projects(No.ZMYJJB-2024-01)of First Exploration Burea,China National Administration of coal Geology.
文摘Under complicated field conditions,such as the coupled effects of freeze-thaw cycles(FTs)and acidification,the leaching behavior of potentially toxic element(PTEs)from indigenous Zn smelting slags(ZSS)was intricately connected to the mineralogy(e.g.,the composition,assemblage,microstructure of mineral particles).In this study,FTs tests were carried out to explore the interactions between PTEs release and ZSSmineralogy.Subsequently,advanced characterization techniqueswere adopted to quantify the mineralogy andmicrostructure of ZSS.The results indicated that ZSS were mainly composed of silicate minerals(e.g.,quartz,biotite and chlorite)and secondary Fe(III)oxyhydroxides(e.g.,magnetite and limonite),accounting for 67.48% and 24.23%,respectively.The occurrence mode analysis revealed that 81.95%of As,21.31%of Pb and 7.77% of Zn were hosted in limonite.About 37.89%,59.34% and 34.50% of Cd,Pb and Zn were associated with carbonate bound fractions.Under FTs interacting with different pH conditions,the leaching concentrations of As,Cd,Cu,Pb and Zn did not significantly increase with the increase in FTs and pH.The microstructure damage of mineral particles in ZSS with the higher porosity was caused by both FTs and proton corrosion.More importantly,the geochemical modeling results suggested that the precipitation of hematite and magnetite,as well as the dissolution of arsenolite,might have little impacts on PTEs release under FTs and FTs with acidification.This work would provide a deeper understanding of PTEs release from smelting waste slags under complex physicochemical interactions.
基金supported by the Yunnan Province Nonferrous Metal Vacuum Metallurgy Top Team[grant number 202305AS350012].
文摘A major problem facing the magnesium melting process is to address the oxidative combustion of magnesium.At present,there are still some problems in the method used to protect magnesium smelting.For example,the reaction of covering flux with magnesium melt is likely to produce a large number of toxic and harmful gasses(Cl_(2) and HCl),the cost of such reaction is high,and there is a lack of clarity on the protection mechanism of CO_(2) acting as the protective gas of magnesium melt.Therefore,a new process is proposed in this paper to isolate the air on the surface of magnesium melt using MgO-C-Mg film.Based on the thermodynamic theory of MgO-C-Mg film formation during crude magnesium smelting,an investigation is conducted into the effect of different experimental conditions on the protective effect of magnesium.Not only is the protective mechanism of MgO-C-Mg film revealed,it is also verified that the MgO-C-Mg film can produce a more pronounced protective effect at suitable temperature.According to thermodynamic analysis,magnesium melt reacts with CO_(2) to form magnesium oxide and C.CO_(2) consumes C when the experimental temperature exceeds 700℃.This is contrary to the purpose of the experiment as it should be maintained at about 700℃.The experimental results show that an obvious protective effect can be produced on the magnesium melt by the MgO-C-Mg film generated under the following conditions of 90%CO_(2)-10%Ar,smelting temperature of 700℃,holding time of 60 min,and stirring time of 20 min.
基金support from the National Key R&D Program of China(Nos.2023YFC3903900,2023YFC3903904)the National Natural Science Foundation of China(Nos.52274343,52174329).
文摘The melting and separation behavior of vanadium-titanium magnetite pellets directed at an efficient extraction of vanadium and titanium was systematically investigated.Applying FactSage simulations and experiments,the smelting separation of three pre-reduced pellets from different regions was analyzed.The simulations demonstrate that FeTi2O5 is converted to TiC at low temperatures,necessitating suppression of this step.Experiments under optimized conditions(1590-1690°C,20-25 min,2%coke,basicity 0.4-0.6,and 3.0%-6.0%MgO)yield iron grade of 92.35%-95.06%,titanium grade of 34.37%-39.89%,and vanadium grade of 0.56%-1.52%,with recoveries of 99.52%-99.60%,94.08%-98.96%,and 92.63%-94.38%for iron,titanium and vanadium,respectively.The titanium in the slag,primarily in the form of anosovite,is suitable for sulfuric acid-based titanium white production.An increase in basicity,MgO content,and pellet metallization serves to improve vanadium recovery in melted iron but lowers the titanium grade in the slag.The overall process effectively utilizes vanadium and titanium resources under optimized conditions.
基金supported by the National Key R&D Program of China(No.2020YFC1909203)the Hunan Provincial Innovation Project,China(No.CX20230213)。
文摘A process for treating cyanide tailings was proposed.The process essentially implicates reduction smelting which involves volatilizing silver,lead,and zinc in the cyanide tailings at high temperatures.Meanwhile,gold and copper combine with the reduced iron to form a metal phase,allowing for the simultaneous recovery of polymetallic elements.The experimental results indicate that the process works optimally with a coke powder of 7.5 wt.%,an alkalinity of 1.0,a melting temperature of 1450℃,and a melting time of 60 min.Under these conditions,more than 99% of gold,77% of copper and 94% of iron are incorporated into pig iron.In the meantime,the volatilization rate of silver exceeds 90%,while lead and zinc are essentially completely volatilized.The primary component of the by-product smelting slag is akermanite,which exhibits lower leaching toxicity than the national standard and belongs to general solid waste.Additionally,taking the trapping process of iron to copper as a case study,the mechanism of iron trapping is methodically examined and divided into three processes:smelting reduction,migration capture,and condensation deposition.
基金Project(JS-211)supported by the State-Owned Enterprise Electric Vehicle Industry Alliance,China
文摘NA novel smelting reduction process based on FeO-SiO2-Al2O3 slag system for spent lithium ion batteries with Al cans was developed, while using copper slag as the only slag former. The feasibility of the process and the mechanism of copper loss in slag were investigated. 98.83% Co, 98.39% Ni and 93.57% Cu were recovered under the optimum conditions of slag former/battery mass ratio of 4.0：1, smelting temperature of 1723 K, and smelting mass ratio of time of 30 min. The FeO-SiO2-Al2O3 slag system for the smelting process is appropriate under the conditions of m（FeO）：m（SiO2）=0.58：1？1.03：1, and 17.19%？21.52% Al2O3 content. The obtained alloy was mainly composed of Fe-Co-Cu-Ni solid solution including small amounts of matte. The obtained slag mainly consisted of fayalite and hercynite. Meanwhile, the mechanism of copper loss is the mechanical entrainment from strip-like fayalite particles in the main form of copper sulfide and metallic copper.
基金Project(41201492)supported by the National Natural Science Foundation of China
文摘A field investigation was performed to study the content, speciation and mobility of vanadium, as well as microbial response in soil from a stone coal smelting district in Hunan province of China. The results showed that the contents of soil V ranged from 168 to 1538 mg/kg, which exceeded the maximum permissible value of Canadian soil quality for V. The mean soil V content from wasteland area reached 1421 mg/kg, and those from the areas related with slag heap, ore pile and smelting center were 380, 260 and 225 mg/kg, respectively. Based on the results of the modified BCR sequential extraction procedure, V contents in the mobile fractions varied from 19.2 to 637 mg/kg accounting for 7.4%-42.3% of total V, and those of V(+5) species were between 21.9 and 534.0 mg/kg. Soil enzyme activity and microbial basal respiration were adversely affected by high level of soil V. More attention should be paid to soil V pollution and potential hazardous surrounding the stone coal smelting district.
基金Project(2008BAB34B01-1)supported by the National Key Technology R&D Program of China
文摘The reduction smelting process for cobalt recovery from converter slag of the Chambishi Copper Smelter in Zambia was studied. The effects of reducing agent dosage, smelting temperature and time and the addition of slag modifiers （CaO and TiO2） were investigated. In addition, the depleted slag and cobalt-bearing alloy were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Under the determined conditions, 94.02% Co, 95.76% Cu and less than 18% Fe in the converter slag were recovered. It was found that the main phases of depleted slag were fayalite and hercynite; and the cobalt-bearing alloy mainly contained metallic copper, Fe-Co-Cu alloys and a small amount of sulfide.
基金Project (50904027) supported by the National Natural Science Foundation of ChinaProject (2013BAB03B05) supported by the National Key Technology R&D Program of China+1 种基金Project (20133BCB23018) supported by the Foundation for Young Scientist(Jinggang Star)of Jiangxi Province,ChinaProject (2012ZBAB206002) supported by the Natural Science Foundation of Jiangxi Province,China
文摘According to the innate characteristic of four types of furnace, the copper flash continuous smelting （CFCS） furnace can be considered a synthetic reactor of two relatively independent processes： flash matte smelting process （FMSP） and copper continuous converting process （CCCP）. Then, the CFCS thermodynamic model was proposed by establishing the multi-phase equilibrium model of FMSP and the local-equilibrium model of CCCP, respectively, and by combining them through the smelting intermediates. Subsequently, the influences of the furnace structures were investigated using the model on the formation of blister copper, the Fe3O4 behavior, the copper loss in slag and the copper recovery rate. The results show that the type D furnace, with double flues and a slag partition wall, is an ideal CFCS reactor compared with the other three types furnaces. For CFCS, it is effective to design a partition wall in the furnace to make FMSP and CCCP perform in two relatively independent zones, respectively, and to make smelting gas and converting gas discharge from respective flues.
基金Project (41271330) supported by the National Natural Science Foundation of China
文摘The effects of moderately thermophilic bacteria on the extraction of metals from zinc smelting slag and electrochemical characteristics of zinc smelting slag carbon paste electrode in bioleaching process were studied. The results show that the extraction rates of Fe, Cu and Zn from the slag reach 86.7%, 90.3% and 66.7% after adsorbed bacteria sterilize, while those with adsorbed bacteria are 91.9%, 96.0% and 84.5% in conditions of pulp density 2%, pH 1.0, temperature 65 °C and stirring rate 120 r/min, respectively. Some stretching peaks of functional groups from bacterial secretes on the bioleached residue surface, such as 1007 cm-1 and 1193 cm-1, turn up through FI-IR analysis and indirectly reveal the presence of the adsorbed bacteria on the slag particles surface. Besides, the corrosion of zinc smelting slag is enhanced by bacteria according to the characteristics of cyclic voltametry and Tafel curves in bioleaching system.
基金Project(2012BAC12B02)supported by the National Key Technology R&D Program of ChinaProject(2014FJ1011)supported by the Key Projects of Science and Technology of Hunan Province,ChinaProject(2011AA061001)supported by the National High-tech Research and Development Program of China
文摘A new process for utilization of hazardous lead-bearing wastes and iron-rich wastes by reducing-matting smelting has been developed.The slag（SG） and the iron-rich matte（IRM） are the main by-products from reducing-matting smelting of lead-bearing wastes and iron-rich wastes.The environmental risk of heavy metals（Cd,Zn,Pb and As） in the main by-products versus the charging material for reducing-matting smelting（CM） has been systematically assessed using leaching toxicity test,the three-stage sequential extraction procedure of European Community Bureau of Reference（BCR） and Hakanson Potential Ecological Risk Index Method（PERI）.The results demonstrate that the ecological risk level of heavy metals for SG and IRM is significantly reduced after the reducing-matting smelting process compared with that for CM.
文摘A mathematical model has been presented to study the combustion of a single copper concentrate particle with high moisture content. By using the presented model, the effect of particle moisture content on particle temperature, sulfur oxidation, and combustion heat generation has been evaluated. The mineralogical composition of the commonly used concentrate at Khatoonabad flash smelting furnace has been used in this study. It was found that the particle moisture content is removed in the sub-second time range and thus the moisture has marginal impact on the variation of particle temperature and on the reaction rate when the gas temperature is assumed to be constant in the reaction shaft. When a concentrate with high moisture content is charged, the particle size enlargement due to the agglomeration of concentrate particles causes an abrupt fall in the particle reaction rate.
