The distribution of the various organic and inorganic constituents and their influences on the combustion of coal has been comprehensively studied.However,the combustion characteristics of pulverized coal depend not o...The distribution of the various organic and inorganic constituents and their influences on the combustion of coal has been comprehensively studied.However,the combustion characteristics of pulverized coal depend not only on rank but also on the composition,distribution,and combination of the macerals.Unlike the proximate and ultimate analyses,determining the macerals in coal involves the use of sophisticated microscopic instrumentation and expertise.In this study,an attempt was made to predict the amount of macerals(vitrinite,inertinite,and liptinite)and total mineral matter from the Witbank Coalfields samples using the multiple input single output white-box artificial neural network(MISOWB-ANN),gene expression programming(GEP),multiple linear regression(MLR),and multiple nonlinear regression(MNLR).The predictive models obtained from the multiple soft computing models adopted are contrasted with one another using difference,efficiency,and composite statistical indicators to examine the appropriateness of the models.The MISOWB-ANN provides a more reliable predictive model than the other three models with the lowest difference and highest efficiency and composite statistical indicators.展开更多
This study explores the extraction of rare earth elements(REEs)from high-ash run-of-mine and discard coal sourced from the Waterberg Coalfield.Three distinct methods were employed:(1)ultrasonic-assisted caustic digest...This study explores the extraction of rare earth elements(REEs)from high-ash run-of-mine and discard coal sourced from the Waterberg Coalfield.Three distinct methods were employed:(1)ultrasonic-assisted caustic digestion;(2)direct acid leaching;and(3)ultrasonic-assisted caustic-acid leaching.Inductively coupled plasma mass spectrometry was utilized to quantify REEs in both the coals and resultant leachates.Leaching the coals with 40%NaOH at 80℃,along with 40 kHz sonication,yielded a total rare earth element(TREE)recovery of less than 2%.Notable enrichment of REEs was observed in the run-of-mine and discard coal by 17%and 19%,respectively.Upon employing 7.5%HCl,a recovery of less than 11.0%for TREE was achieved in both coal samples.However,leaching the caustic digested coal samples with 7.5%HCl significantly enhanced the TREE recovery to 88.8%and 80.0%for run-of-mine and discard coal,respectively.X-ray diffraction analysis identified kaolinite and quartz as the predominant minerals.Scanning electron microscopyenergy dispersive microanalysis revealed monazite and xenotime as the REE-bearing minerals within the coal samples.These minerals were found either liberated,attached to,or encapsulated by the clay-quartz matrices.Further mineralogical assessments highlighted the increased REE concentrations in coals post-caustic digestion and subsequent recovery during acid leaching.This increase was attributed to the partial dissolution of kaolinite encapsulating the RE-phosphates and the digestion of REE-bearing minerals.Notably,undissolved REE-bearing elements in the caustic-acid-leached coal indicated the necessity of harsh leaching conditions to augment REE recovery from these coal samples.展开更多
In this study,we have determined the main important physical and chemical properties as well as the heavy metal concentrations of the primary and secondary wastewater treatment sludge from a pulp and board mill comple...In this study,we have determined the main important physical and chemical properties as well as the heavy metal concentrations of the primary and secondary wastewater treatment sludge from a pulp and board mill complex located in Finland in order to evaluate the utilization of these by-products as a soil amendment agent or a fertilizer product.Easily soluble Ca,Mg,K,Na,P and S concentrations in the sludges were extracted by ammonium acetate(CH3COONH4)and easily soluble Cu,Mn and Zn concentrations by CH3COONH4+Na2EDTA.For the determination of total nutrient and total heavy metal concentrations in sludges,they were digested using aqua regia(3 mL HCl+9 mL HNO3).The total heavy concentrations in the primary sludge were lower than the Finnish heavy metal limit values for fertilizer products.In the secondary sludge,all other total heavy metals than the total Cd concentration(4.8 mg/kg;d.w.)were lower than the heavy metal limit values for fertilizer products.Due to the low total heavy metal concentrations,which were lower than the Finnish limit values for fertilizer products,the primary sludge is a potential fertilizer.Although the total Cd concentration(4.8 mg/kg;d.w.)in the secondary sludge exceed the limit value of 1.5 mg/kg(d.w.)for fertilizer products,this residue may be used as a soil improver,a growing media or as a fertilizer product in landfill sites or in other closed industrial areas,because the Finnish limit values for fertilizer products are not applied at these sites.展开更多
Hydrothermal carbonization(HTC)technologies for producing value-added carbonaceous material(hydrochar)from coal waste and sewage sludge(SS)waste might be a long-term recycling strategy for hydrogen storage application...Hydrothermal carbonization(HTC)technologies for producing value-added carbonaceous material(hydrochar)from coal waste and sewage sludge(SS)waste might be a long-term recycling strategy for hydrogen storage applications,cutting disposal costs and solving waste disposal difficulties.In this study,hydrochars(HC)with high carbon content were produced using a combination of optimal HTC(HTC and Co-HTC)and chemical activation of coal tailings(CT),coal slurry(CS),and a mixture of coal discard and sewage sludge(CB).At 850℃and 800℃,respectively,with a KOH/HC ratio of 4:1 and a residence time of 135 min,activated carbons(ACs)with the highest Brunauer–Emmett–Teller specific surface(S_(BET))of 2299.25 m^(2)g^(−1)and 2243.57 m^(2)g^(−1)were obtained.The hydrogen adsorption capability of the produced ACs was further studied using gas adsorption isotherms at 77 K.At 35 bars,the values of hydrogen adsorbed onto AC-HCT(AC obtained from HTC of CT),AC-HCS(AC obtained from HTC of CS),and AC-HCB(AC obtained from HTC of the blending of coal discard(CD)and SS)were approximately 6.12%,6.8%,and 6.57%in weight,respectively.Furthermore,the cost of producing synthetic ACs for hydrogen storage is equivalent to the cost of commercial carbons.Furthermore,the high proportion of carbon retained(>70%)in ACs synthesized by HTC from CD and SS precursors should restrict their potential carbon emissions.展开更多
文摘The distribution of the various organic and inorganic constituents and their influences on the combustion of coal has been comprehensively studied.However,the combustion characteristics of pulverized coal depend not only on rank but also on the composition,distribution,and combination of the macerals.Unlike the proximate and ultimate analyses,determining the macerals in coal involves the use of sophisticated microscopic instrumentation and expertise.In this study,an attempt was made to predict the amount of macerals(vitrinite,inertinite,and liptinite)and total mineral matter from the Witbank Coalfields samples using the multiple input single output white-box artificial neural network(MISOWB-ANN),gene expression programming(GEP),multiple linear regression(MLR),and multiple nonlinear regression(MNLR).The predictive models obtained from the multiple soft computing models adopted are contrasted with one another using difference,efficiency,and composite statistical indicators to examine the appropriateness of the models.The MISOWB-ANN provides a more reliable predictive model than the other three models with the lowest difference and highest efficiency and composite statistical indicators.
基金The research was also supported by the National Research Foundation(NRF)of South Africa's SARChI Clean Coal Technology Grant(86421)。
文摘This study explores the extraction of rare earth elements(REEs)from high-ash run-of-mine and discard coal sourced from the Waterberg Coalfield.Three distinct methods were employed:(1)ultrasonic-assisted caustic digestion;(2)direct acid leaching;and(3)ultrasonic-assisted caustic-acid leaching.Inductively coupled plasma mass spectrometry was utilized to quantify REEs in both the coals and resultant leachates.Leaching the coals with 40%NaOH at 80℃,along with 40 kHz sonication,yielded a total rare earth element(TREE)recovery of less than 2%.Notable enrichment of REEs was observed in the run-of-mine and discard coal by 17%and 19%,respectively.Upon employing 7.5%HCl,a recovery of less than 11.0%for TREE was achieved in both coal samples.However,leaching the caustic digested coal samples with 7.5%HCl significantly enhanced the TREE recovery to 88.8%and 80.0%for run-of-mine and discard coal,respectively.X-ray diffraction analysis identified kaolinite and quartz as the predominant minerals.Scanning electron microscopyenergy dispersive microanalysis revealed monazite and xenotime as the REE-bearing minerals within the coal samples.These minerals were found either liberated,attached to,or encapsulated by the clay-quartz matrices.Further mineralogical assessments highlighted the increased REE concentrations in coals post-caustic digestion and subsequent recovery during acid leaching.This increase was attributed to the partial dissolution of kaolinite encapsulating the RE-phosphates and the digestion of REE-bearing minerals.Notably,undissolved REE-bearing elements in the caustic-acid-leached coal indicated the necessity of harsh leaching conditions to augment REE recovery from these coal samples.
文摘In this study,we have determined the main important physical and chemical properties as well as the heavy metal concentrations of the primary and secondary wastewater treatment sludge from a pulp and board mill complex located in Finland in order to evaluate the utilization of these by-products as a soil amendment agent or a fertilizer product.Easily soluble Ca,Mg,K,Na,P and S concentrations in the sludges were extracted by ammonium acetate(CH3COONH4)and easily soluble Cu,Mn and Zn concentrations by CH3COONH4+Na2EDTA.For the determination of total nutrient and total heavy metal concentrations in sludges,they were digested using aqua regia(3 mL HCl+9 mL HNO3).The total heavy concentrations in the primary sludge were lower than the Finnish heavy metal limit values for fertilizer products.In the secondary sludge,all other total heavy metals than the total Cd concentration(4.8 mg/kg;d.w.)were lower than the heavy metal limit values for fertilizer products.Due to the low total heavy metal concentrations,which were lower than the Finnish limit values for fertilizer products,the primary sludge is a potential fertilizer.Although the total Cd concentration(4.8 mg/kg;d.w.)in the secondary sludge exceed the limit value of 1.5 mg/kg(d.w.)for fertilizer products,this residue may be used as a soil improver,a growing media or as a fertilizer product in landfill sites or in other closed industrial areas,because the Finnish limit values for fertilizer products are not applied at these sites.
文摘Hydrothermal carbonization(HTC)technologies for producing value-added carbonaceous material(hydrochar)from coal waste and sewage sludge(SS)waste might be a long-term recycling strategy for hydrogen storage applications,cutting disposal costs and solving waste disposal difficulties.In this study,hydrochars(HC)with high carbon content were produced using a combination of optimal HTC(HTC and Co-HTC)and chemical activation of coal tailings(CT),coal slurry(CS),and a mixture of coal discard and sewage sludge(CB).At 850℃and 800℃,respectively,with a KOH/HC ratio of 4:1 and a residence time of 135 min,activated carbons(ACs)with the highest Brunauer–Emmett–Teller specific surface(S_(BET))of 2299.25 m^(2)g^(−1)and 2243.57 m^(2)g^(−1)were obtained.The hydrogen adsorption capability of the produced ACs was further studied using gas adsorption isotherms at 77 K.At 35 bars,the values of hydrogen adsorbed onto AC-HCT(AC obtained from HTC of CT),AC-HCS(AC obtained from HTC of CS),and AC-HCB(AC obtained from HTC of the blending of coal discard(CD)and SS)were approximately 6.12%,6.8%,and 6.57%in weight,respectively.Furthermore,the cost of producing synthetic ACs for hydrogen storage is equivalent to the cost of commercial carbons.Furthermore,the high proportion of carbon retained(>70%)in ACs synthesized by HTC from CD and SS precursors should restrict their potential carbon emissions.
