Interactions of N, P and K fertilizers in soil-plant systems are widelyrecognized. This study focused on the transformations of monocalcium phosphate (Ca(H_2PO_4)_2) (MCP)with co-application of ammonium and potassium ...Interactions of N, P and K fertilizers in soil-plant systems are widelyrecognized. This study focused on the transformations of monocalcium phosphate (Ca(H_2PO_4)_2) (MCP)with co-application of ammonium and potassium fertilizers in three different soils. The resultsshowed that after 1 d incubation a large portion of the MCP applied in the paddy, calcareous and redsoils became the water-insoluble form and the recoveries of P applied as Olsen P varied greatly inthese three soils. Application of ammonium sulfate ((NH_4)_2SO_4) (AS) or potassium chloride (KCl)reduced WSP significantly the soils with AS more effective than KCl in the calcareous soil, whilethe reverse occurred in the red soil. Meanwhile, in the paddy soil, co-application of the twofertilizers reduced WSP more than when the fertilizers were applied individually. The co-applicationof AS with MCP in the paddy and calcareous soils significantly reduced Olsen P, but the oppositeoccurred in the red soil. The experiment on the effect of different accompanying anions showed thatthe ammonium fertilizers (PNCl and PNS) reduced WSP more effectively than the correspondingpotassium fertilizers (PKCl and PKS) in the calcareous soil due to the difference of the cations,whereas in the red soil, the chlorides reduced WSP more effectively than the sulfates. Overall,co-application of ammonium or potassium fertilizers with MCP significantly decreased availability ofP from MCP during its transformation in soils, especially when MCP was applied in combination withammonium in the calcareous soil.展开更多
When humic acid (HA) and phosphorus (P) fertilizer are simultaneously applied to soil, HA may affect the movement of P. A laboratory incubation experiment was conducted to quantify the effects of a commercial HA produ...When humic acid (HA) and phosphorus (P) fertilizer are simultaneously applied to soil, HA may affect the movement of P. A laboratory incubation experiment was conducted to quantify the effects of a commercial HA product co-applied with monocalcium phosphate (MCP) on the distance of P movement and the concentration of P in various forms at different distances from the P fertilizer application site in a calcareous soil from northern China. Fertilizer MCP (at a rate equivalent to 26.6 kg P ha-1 ) was applied alone or in combination with HA (at 254.8 kg HA ha-1 ) to the surface of soil packed in cylinders (150 mm high and 50 mm internal diameter), and then incubated at 320 g kg-1 moisture content for 7 and 28 d periods. Extraction and analysis of each 2 mm soil layer in columns showed that the addition of HA to MCP increased the distance of P movement and the concentrations of water-extractable P, acid-extractable P and Olsen P in soil. The addition of HA to MCP could enhance P availability by increasing the distance of P movement and the concentration of extractable P in soil surrounding the P fertilizer.展开更多
Phosphate rock has been considered as one of the potential promising resources for rare earth elements(REEs). But the cost issues and the technical challenges caused by the low content of REEs in ores did hinder the f...Phosphate rock has been considered as one of the potential promising resources for rare earth elements(REEs). But the cost issues and the technical challenges caused by the low content of REEs in ores did hinder the further development of REEs recovery technologies. In order to explore a green process for the recovery of REEs from phosphate rock, this study investigates the effects of phosphoric acid concentration, liquid-to-solid ratio(L/S ratio), leaching time and temperature on the leaching efficiencies of the major components from phosphate rock. A REEs recovery of 94.3% and a phosphorus recovery of 95.3%are achieved under the optimal conditions of attacking phosphate rock using 30%P_2 O_5 acid with an L/S ratio of 10:1 and a stirring speed of 250 r/min at 25 ℃ for 4 h. Then,the selective precipitation of REEs with 81.3% REEs recovery is realized by heating up the leaching solution from 25 to 90 ℃ and keeping for4 h. Thereafter, more than 95% phosphoric acid is recovered by H_2 SO_4 and high purity gypsum, more than95% CaSO_4(tested by XRF), is also produced at the same time. Ultimately, a green process that leaches phosphate rock with H_3 PO_4, selectively precipitates REEs from leaching solution by heating up, recovers H_3 PO_4 with H2 SO4 is proposed. Compared with REE recovery in traditional processes, this process owns the merits of simple operation, energy saving and minimum wastes.展开更多
In order to achieve deeper understanding of rare earth elements(REEs) behaviors during phosphate rock processing with H_3PO_4. The solubility of REEs in Ca(H_2PO_4)_2-H_3PO_4 solutions with various concentrations of C...In order to achieve deeper understanding of rare earth elements(REEs) behaviors during phosphate rock processing with H_3PO_4. The solubility of REEs in Ca(H_2PO_4)_2-H_3PO_4 solutions with various concentrations of Ca(H_2PO_4)_2 at different temperatures were tested. The results demonstrate that REEs solubility decreases sharply with the increasing concentration of Ca(H_2PO_4)_2. Equations between [REE^(3+)] and [H^+],[H^+] and [Ca^(2+)] in Ca(H_2PO_4)_2-H_3PO_4 solutions were built based on the precipitation-dissolution equilibrium of rare earth phosphates and the ionization equilibrium of H_3PO_4. According to the equations, the decreasing mechanism of REEs solubility caused by elevated concentration of Ca(H_2PO_4)_2 was determined. The mechanism can be illustrated as that the elevated concentration of [H_2 PO_4^-] decreases the concentration of hydrogen ion by retarding the ionization process of H_3PO_4 and directly promotes the precipitation of rare earth phosphates. Furthermore, it can be easy deduced that similar effect would be caused by the other cation impurities(Fe^(3+), Al^(3+), etc.) on REEs solubility based on the mechanism. In addition, superimposed reduction effect on REEs solubility caused by the elevated concentration of Ca(H_2PO_4)_2 and the elevated temperature is found. This superimposed effect leads to a super low solubility of REEs in Ca(H_2PO_4)_2-H_3PO_4 solution. On the basis of the experimental study, outlooks and suggestions for further development of REEs recovery method are given.展开更多
Two kinds of CACs with different monocalcium aluminate（CA） contents were used in the PC/CAC（PAC） mixtures. Effects of CA and CACs on the properties of PAC were analyzed by setting times and the compressive strengt...Two kinds of CACs with different monocalcium aluminate（CA） contents were used in the PC/CAC（PAC） mixtures. Effects of CA and CACs on the properties of PAC were analyzed by setting times and the compressive strength tests, and also by means of calorimetry, XRD, DTA-TG and ESEM. The experimental results show that the compressive strength of the PAC mortars decreases with increasing content of CAC while it declines sharply with a higher content of CA in CAC. Compared with neat PC paste, the content of calcium hydroxide in hydrates of PAC paste decreases significantly, and the hydration time of PC is prominently prolonged. Additionally, the higher the content of CA in CAC, the more obviously the hydration of PC is delayed, confi rming that the CA phase in CAC plays an important role in the delay of PC hydration.展开更多
基金Project supported by the National Natural Science Foundation of China (No. 40071051) the National Key Basic Research Support Foundation of China (No. G1999011802).
文摘Interactions of N, P and K fertilizers in soil-plant systems are widelyrecognized. This study focused on the transformations of monocalcium phosphate (Ca(H_2PO_4)_2) (MCP)with co-application of ammonium and potassium fertilizers in three different soils. The resultsshowed that after 1 d incubation a large portion of the MCP applied in the paddy, calcareous and redsoils became the water-insoluble form and the recoveries of P applied as Olsen P varied greatly inthese three soils. Application of ammonium sulfate ((NH_4)_2SO_4) (AS) or potassium chloride (KCl)reduced WSP significantly the soils with AS more effective than KCl in the calcareous soil, whilethe reverse occurred in the red soil. Meanwhile, in the paddy soil, co-application of the twofertilizers reduced WSP more than when the fertilizers were applied individually. The co-applicationof AS with MCP in the paddy and calcareous soils significantly reduced Olsen P, but the oppositeoccurred in the red soil. The experiment on the effect of different accompanying anions showed thatthe ammonium fertilizers (PNCl and PNS) reduced WSP more effectively than the correspondingpotassium fertilizers (PKCl and PKS) in the calcareous soil due to the difference of the cations,whereas in the red soil, the chlorides reduced WSP more effectively than the sulfates. Overall,co-application of ammonium or potassium fertilizers with MCP significantly decreased availability ofP from MCP during its transformation in soils, especially when MCP was applied in combination withammonium in the calcareous soil.
基金Supported by the Shandong Provincial Doctoral Foundation of China(Nos.2007BS08013 and BS2012NY011)
文摘When humic acid (HA) and phosphorus (P) fertilizer are simultaneously applied to soil, HA may affect the movement of P. A laboratory incubation experiment was conducted to quantify the effects of a commercial HA product co-applied with monocalcium phosphate (MCP) on the distance of P movement and the concentration of P in various forms at different distances from the P fertilizer application site in a calcareous soil from northern China. Fertilizer MCP (at a rate equivalent to 26.6 kg P ha-1 ) was applied alone or in combination with HA (at 254.8 kg HA ha-1 ) to the surface of soil packed in cylinders (150 mm high and 50 mm internal diameter), and then incubated at 320 g kg-1 moisture content for 7 and 28 d periods. Extraction and analysis of each 2 mm soil layer in columns showed that the addition of HA to MCP increased the distance of P movement and the concentrations of water-extractable P, acid-extractable P and Olsen P in soil. The addition of HA to MCP could enhance P availability by increasing the distance of P movement and the concentration of extractable P in soil surrounding the P fertilizer.
基金Project supported by the National Natural Science Foundation of China(51674036)the Beijing Nova Program(Z161100004916108)
文摘Phosphate rock has been considered as one of the potential promising resources for rare earth elements(REEs). But the cost issues and the technical challenges caused by the low content of REEs in ores did hinder the further development of REEs recovery technologies. In order to explore a green process for the recovery of REEs from phosphate rock, this study investigates the effects of phosphoric acid concentration, liquid-to-solid ratio(L/S ratio), leaching time and temperature on the leaching efficiencies of the major components from phosphate rock. A REEs recovery of 94.3% and a phosphorus recovery of 95.3%are achieved under the optimal conditions of attacking phosphate rock using 30%P_2 O_5 acid with an L/S ratio of 10:1 and a stirring speed of 250 r/min at 25 ℃ for 4 h. Then,the selective precipitation of REEs with 81.3% REEs recovery is realized by heating up the leaching solution from 25 to 90 ℃ and keeping for4 h. Thereafter, more than 95% phosphoric acid is recovered by H_2 SO_4 and high purity gypsum, more than95% CaSO_4(tested by XRF), is also produced at the same time. Ultimately, a green process that leaches phosphate rock with H_3 PO_4, selectively precipitates REEs from leaching solution by heating up, recovers H_3 PO_4 with H2 SO4 is proposed. Compared with REE recovery in traditional processes, this process owns the merits of simple operation, energy saving and minimum wastes.
基金Project supported by National Natural Science Foundation of China(51674036)Beijing Nova Program(Z161100004916108)
文摘In order to achieve deeper understanding of rare earth elements(REEs) behaviors during phosphate rock processing with H_3PO_4. The solubility of REEs in Ca(H_2PO_4)_2-H_3PO_4 solutions with various concentrations of Ca(H_2PO_4)_2 at different temperatures were tested. The results demonstrate that REEs solubility decreases sharply with the increasing concentration of Ca(H_2PO_4)_2. Equations between [REE^(3+)] and [H^+],[H^+] and [Ca^(2+)] in Ca(H_2PO_4)_2-H_3PO_4 solutions were built based on the precipitation-dissolution equilibrium of rare earth phosphates and the ionization equilibrium of H_3PO_4. According to the equations, the decreasing mechanism of REEs solubility caused by elevated concentration of Ca(H_2PO_4)_2 was determined. The mechanism can be illustrated as that the elevated concentration of [H_2 PO_4^-] decreases the concentration of hydrogen ion by retarding the ionization process of H_3PO_4 and directly promotes the precipitation of rare earth phosphates. Furthermore, it can be easy deduced that similar effect would be caused by the other cation impurities(Fe^(3+), Al^(3+), etc.) on REEs solubility based on the mechanism. In addition, superimposed reduction effect on REEs solubility caused by the elevated concentration of Ca(H_2PO_4)_2 and the elevated temperature is found. This superimposed effect leads to a super low solubility of REEs in Ca(H_2PO_4)_2-H_3PO_4 solution. On the basis of the experimental study, outlooks and suggestions for further development of REEs recovery method are given.
基金Funded by the National Key Technology R&D Programs in the12th Five-year Plan of China(2012BA20B02)
文摘Two kinds of CACs with different monocalcium aluminate（CA） contents were used in the PC/CAC（PAC） mixtures. Effects of CA and CACs on the properties of PAC were analyzed by setting times and the compressive strength tests, and also by means of calorimetry, XRD, DTA-TG and ESEM. The experimental results show that the compressive strength of the PAC mortars decreases with increasing content of CAC while it declines sharply with a higher content of CA in CAC. Compared with neat PC paste, the content of calcium hydroxide in hydrates of PAC paste decreases significantly, and the hydration time of PC is prominently prolonged. Additionally, the higher the content of CA in CAC, the more obviously the hydration of PC is delayed, confi rming that the CA phase in CAC plays an important role in the delay of PC hydration.
