In this study, a method for preparing pure manganese sulfate from low-grade ores with a granule mean size of 0.47 mm by direct acid leaching was developed. The effects of the types of leaching agents, sulfitric acid c...In this study, a method for preparing pure manganese sulfate from low-grade ores with a granule mean size of 0.47 mm by direct acid leaching was developed. The effects of the types of leaching agents, sulfitric acid concentration, reaction temperature, and agitation rate on the leaching efficiency of manganese were investigated. We observed that sulfuric acid used as a leaching agent provides a similar leach- ing efficiency of manganese and superior selectivity against calcium compared to hydrochloric acid. The optimal leaching conditions in sul- furic acid media were determined; under the optimal conditions, the leaching efficiencies of Mn and Ca were 92.42% and 9.61%, respec- tively. Moreover, the kinetics of manganese leaching indicated that the leaching follows the diffusion-controlled model with an apparent ac- tivation energy of 12.28 kJ·mol-l. The purification conditions of the leaching solution were also discussed. The results show that manganese dioxide is a suitable oxidant of ferrous ions and sodium dimethyldithiocarbamate is an effective precipitant of heavy metals. Finally, through chemical analysis and X-ray diffraction analysis, the obtained product was determined to contain 98% of MnSOa4·H20.展开更多
Organic and inorganic carbon contents of marine sediments are important to reconstruct marine productivity,global carbon cycle, and climate change. A proper method to separate and determine organic and inorganic carbo...Organic and inorganic carbon contents of marine sediments are important to reconstruct marine productivity,global carbon cycle, and climate change. A proper method to separate and determine organic and inorganic carbons is thus of great necessity. Although the best method is still disputable, the acid leaching method is widely used in many laboratories because of its ease-of-use and high accuracy. The results of the elemental analysis of sediment trap samples reveal that organic and inorganic carbon contents cannot be obtained using the acid leaching method, causing an infinitely amplified error when the carbon content of the decarbonated sample is 12%±1% according to a mathematical derivation. Acid fumigation and gasometric methods are used for comparison, which indicates that other methods can avoid this problem in organic carbon analysis. For the first time, this study uncovers the pitfalls of the acid leaching method, which limits the implication in practical laboratory measurement, and recommends alternative solutions of organic/inorganic carbon determination in marine sediments.展开更多
Chicken manure was composted for 110 d to evaluate changes in organic carbon (C) and humic substance-complexed copper (HS-Cu) extracted with water,sodium hydroxide (NaOH),and sodium pyrophosphate and sodium hydroxide ...Chicken manure was composted for 110 d to evaluate changes in organic carbon (C) and humic substance-complexed copper (HS-Cu) extracted with water,sodium hydroxide (NaOH),and sodium pyrophosphate and sodium hydroxide mixture (Na 4 P 2 O 7-NaOH).The average HS-Cu content from the Na 4 P 2 O 7-NaOH extraction accounted for 46.8% of the total Cu in the compost,followed by those from the NaOH and water extractions,which accounted for 34.5% and 6% of the total Cu in the compost,respectively.NaOH-Na 4 P 2 O 7-extractable HS-Cu increased throughout the composting process.NaOH-extractable HS-Cu increased during the first 50 d of composting and then leveled off.Water-extractable HS-Cu enhanced during the first 21 d and then decreased.Water-extractable HS-Cu was not correlated to NaOH-or NaOH-Na 4 P 2 O 7-extractable organic C.The average amount of Cu leached from the compost was about 20% of the total Cu in the chicken manure and Cu leaching increased during the first 35 d of composting and then decreased.Leaching of Cu was significantly correlated to the concentrations of HS-Cu extracted with NaOH and water,but was not correlated to the concentration of HS-Cu extracted with NaOH-Na 4 P 2 O 7.Thus,NaOH-and water-extractable HS-Cu were relatively labile and NaOH-Na 4 P 2 O 7-extractable HS-Cu was relatively immobile.Composting process after rapid decomposition could result in low potential of Cu leaching because of formation of more NaOH-Na 4 P 2 O 7-extractable HS-Cu.展开更多
A hydrometallurgical process to extract silver from the silver-lead ore in Boorchi,Mongolia by using thiourea leaching solution is studied in this work.Through the observation of optical and scanning electron microsco...A hydrometallurgical process to extract silver from the silver-lead ore in Boorchi,Mongolia by using thiourea leaching solution is studied in this work.Through the observation of optical and scanning electron microscopes,and energy spectral analysis,it is determined that 5 kinds of silver minerals exist in the ore,including argentite,Ag-tetrahedrite,Ag-Zn-Sb-tetrahedrite,freibergite and acanthite.The experimental results of direct thiourea leaching of the ore show that 56%~60% of silver is leached.The main reason for the low leaching rate is due to silver minerals enveloped in galena and other minerals,even though the ore is ground to the particle size of 75μm.When the ore is pretreated with ammonium carbonate solution under oxidation,the experimental results of thiourea leaching show that the leaching rate of silver increases to near 75% with the pretreatment.Based on the leaching experiments,a principle hydrometallurgical technological route to extract silver from the Ag-Pb ore is proposed.展开更多
The newly developed green leaching processes for chromium, lead and gold extraction from ores or concentrates are described. The chromium is extracted from the iron chromite ore with fused sodium hydroxide at 500-550...The newly developed green leaching processes for chromium, lead and gold extraction from ores or concentrates are described. The chromium is extracted from the iron chromite ore with fused sodium hydroxide at 500-550°C as sodium chromate. The galena in lead sulfide concentrate is converted into lead carbonate in ammonium or sodium carbonate solution at 50-80°C followed by the separation of lead carbonate formed from the unconverted sulfide ores by flotation. Gold associated with sulfide ore (such as pyrite and chalcopyrite) can be extracted into sodium thiosulfate solution without any pretreatment such as roasting, high pressure aqueous oxidation or bacteria pre-leaching.展开更多
Fluorinated rare earth molten-salt electrolytic slag contains a considerable amount of rare earth elements,as well as a variety of heavy metals and fluorides that cause environmental pollution.Therefore,it is of great...Fluorinated rare earth molten-salt electrolytic slag contains a considerable amount of rare earth elements,as well as a variety of heavy metals and fluorides that cause environmental pollution.Therefore,it is of great importance to fully utilise this resource.In this study,the transformation mechanism of fluorinated rare earth molten-salt electrolytic slag roasted with sodium carbonate,and the regulation mechanism of rare earth leaching under different roasting conditions were investigated with the help of thermodynamic calculation of the reactions and kinetic analysis.The thermodynamic and differential thermal thermogravimetric(DTA-TG)analysis shows that the transformation of rare earth fluoride to rare earth oxide is promoted at elevated temperature.Furthermore,the leaching experimental results show that increasing the temperature,time,hydrochloric acid concentration,and liquid-solid ratio can effectively promote the recovery of rare earths.The optimum experimental conditions are a roasting temperature of 700℃,roasting time of 2 h,and sodium carbonate to molten salt electrolytic slag mass ratio of 0.6,followed by leaching at 80℃with a liquid-solid ratio of 10:1 by adding 3 moI/L hydrochlo ric acid with stirring for 2 h.Under these conditions,the rare earths in the molten salt electrolytic slag are biologically transformed at a lower temperature and the leaching efficiency of rare earths exceeds 98%.展开更多
This paper critically reviewed the current knowledge and challenges of rice husk biochar(RHB)production and its effects on soil properties,plant growth,immobilization of heavy metals,reduction of nutrient leaching and...This paper critically reviewed the current knowledge and challenges of rice husk biochar(RHB)production and its effects on soil properties,plant growth,immobilization of heavy metals,reduction of nutrient leaching and mitigation of greenhouse gas emissions.The characteristics of RHBs produced at various pyrolysis temperatures were discussed and compared to biochars derived from other agro-industrial wastes.RHBs produced at higher pyrolysis temperatures show lower hydrogen/carbon ratio,which suggests the presence of higher aromatic carbon compounds.The increase of pyrolysis temperature also results in production of RHBs with higher ash content,lower yield and higher surface area.RHB usually has higher silicon and ash contents and lower carbon content compared to biochars derived from other feedstocks at the same pyrolysis conditions.Although it depends on soil type,RHB application can improve soil organic carbon content,cation exchange capacity,available K concentration,bulk density and microbial activity.The effect of RHB on soil aggregation mainly depends on soil texture.The growth of different crops is also enhanced by application of RHB.RHB addition to soil can immobilize heavy metals and herbicides and reduce their bioavailability.RHB application shows a significant capacity in reduction of nitrate leaching,although its magnitude depends on the biochar application rate and soil biogeochemical characteristics.Use of RHB,especially in paddy fields,shows a promising mitigation effect on greenhouse gas(CH4,CO2 and N2O)emissions.Although RHB characteristics are also related to other factors such as pyrolysis heating rate and residence time,its performance for specific applications(e.g.carbon sequestration,pH amendment)can be manipulated by adjusting the pyrolysis temperature.More research is needed on long-term field applications of RHB to fully understand the advantages and disadvantages of RHB as a soil amendment.展开更多
A laboratory lysimeter experiment was conducted to investigate the effects of forage corn (Zea mays L.) stalk application on the CO2 concentration in soil air and calcareous sodic soil reclamation. The experimental tr...A laboratory lysimeter experiment was conducted to investigate the effects of forage corn (Zea mays L.) stalk application on the CO2 concentration in soil air and calcareous sodic soil reclamation. The experimental treatments tested were soil exchangeable sodium percentage (ESP) levels of 1, 11, and 19, added corn stalk contents of 0 to 36 g kg-1, and incubation durations of 30 and 60 days. The experimental results indicated that corn stalk application and incubation significantly increased CO2 partial pressure in soil profile and lowered pH value in soil solution, subsequently increased native CaCO3 mineral dissolution and electrolyte concentration of soil solution, and finally significantly contributed to reduction on soil sodicity level. The reclamation effciency of calcareous sodic soils increased with the added corn stalk. When corn stalks were added at the rates of 22 and 34 g kg-1 into the soil with initial ESP of 19, its ESP value was decreased by 56% and 78%, respectively, after incubation of 60 days and the leaching of 6.5 pore volumes (about 48 L of percolation water) with distilled water. Therefore, crop stalk application and incubation could be used as a choice to reclaim moderate calcareous sodic soils or as a supplement of phytoremediation to improve reclamation effciency.展开更多
基金supported by the National Natural Science Foundation of China (51374249)
文摘In this study, a method for preparing pure manganese sulfate from low-grade ores with a granule mean size of 0.47 mm by direct acid leaching was developed. The effects of the types of leaching agents, sulfitric acid concentration, reaction temperature, and agitation rate on the leaching efficiency of manganese were investigated. We observed that sulfuric acid used as a leaching agent provides a similar leach- ing efficiency of manganese and superior selectivity against calcium compared to hydrochloric acid. The optimal leaching conditions in sul- furic acid media were determined; under the optimal conditions, the leaching efficiencies of Mn and Ca were 92.42% and 9.61%, respec- tively. Moreover, the kinetics of manganese leaching indicated that the leaching follows the diffusion-controlled model with an apparent ac- tivation energy of 12.28 kJ·mol-l. The purification conditions of the leaching solution were also discussed. The results show that manganese dioxide is a suitable oxidant of ferrous ions and sodium dimethyldithiocarbamate is an effective precipitant of heavy metals. Finally, through chemical analysis and X-ray diffraction analysis, the obtained product was determined to contain 98% of MnSOa4·H20.
基金The National Natural Science Foundation of China under contract Nos 41530964,41776047,41876048 and 91528304。
文摘Organic and inorganic carbon contents of marine sediments are important to reconstruct marine productivity,global carbon cycle, and climate change. A proper method to separate and determine organic and inorganic carbons is thus of great necessity. Although the best method is still disputable, the acid leaching method is widely used in many laboratories because of its ease-of-use and high accuracy. The results of the elemental analysis of sediment trap samples reveal that organic and inorganic carbon contents cannot be obtained using the acid leaching method, causing an infinitely amplified error when the carbon content of the decarbonated sample is 12%±1% according to a mathematical derivation. Acid fumigation and gasometric methods are used for comparison, which indicates that other methods can avoid this problem in organic carbon analysis. For the first time, this study uncovers the pitfalls of the acid leaching method, which limits the implication in practical laboratory measurement, and recommends alternative solutions of organic/inorganic carbon determination in marine sediments.
基金Project supported by the Ministry of Science and Technology of China (No. 2007BAD89B16)the National Natural Science Foundation of China (No. 39800093)+1 种基金the National Undergraduate Innovational Experimentation Program of Chinathe Youth Planning Program of Northwest A & F University,China
文摘Chicken manure was composted for 110 d to evaluate changes in organic carbon (C) and humic substance-complexed copper (HS-Cu) extracted with water,sodium hydroxide (NaOH),and sodium pyrophosphate and sodium hydroxide mixture (Na 4 P 2 O 7-NaOH).The average HS-Cu content from the Na 4 P 2 O 7-NaOH extraction accounted for 46.8% of the total Cu in the compost,followed by those from the NaOH and water extractions,which accounted for 34.5% and 6% of the total Cu in the compost,respectively.NaOH-Na 4 P 2 O 7-extractable HS-Cu increased throughout the composting process.NaOH-extractable HS-Cu increased during the first 50 d of composting and then leveled off.Water-extractable HS-Cu enhanced during the first 21 d and then decreased.Water-extractable HS-Cu was not correlated to NaOH-or NaOH-Na 4 P 2 O 7-extractable organic C.The average amount of Cu leached from the compost was about 20% of the total Cu in the chicken manure and Cu leaching increased during the first 35 d of composting and then decreased.Leaching of Cu was significantly correlated to the concentrations of HS-Cu extracted with NaOH and water,but was not correlated to the concentration of HS-Cu extracted with NaOH-Na 4 P 2 O 7.Thus,NaOH-and water-extractable HS-Cu were relatively labile and NaOH-Na 4 P 2 O 7-extractable HS-Cu was relatively immobile.Composting process after rapid decomposition could result in low potential of Cu leaching because of formation of more NaOH-Na 4 P 2 O 7-extractable HS-Cu.
文摘A hydrometallurgical process to extract silver from the silver-lead ore in Boorchi,Mongolia by using thiourea leaching solution is studied in this work.Through the observation of optical and scanning electron microscopes,and energy spectral analysis,it is determined that 5 kinds of silver minerals exist in the ore,including argentite,Ag-tetrahedrite,Ag-Zn-Sb-tetrahedrite,freibergite and acanthite.The experimental results of direct thiourea leaching of the ore show that 56%~60% of silver is leached.The main reason for the low leaching rate is due to silver minerals enveloped in galena and other minerals,even though the ore is ground to the particle size of 75μm.When the ore is pretreated with ammonium carbonate solution under oxidation,the experimental results of thiourea leaching show that the leaching rate of silver increases to near 75% with the pretreatment.Based on the leaching experiments,a principle hydrometallurgical technological route to extract silver from the Ag-Pb ore is proposed.
文摘The newly developed green leaching processes for chromium, lead and gold extraction from ores or concentrates are described. The chromium is extracted from the iron chromite ore with fused sodium hydroxide at 500-550°C as sodium chromate. The galena in lead sulfide concentrate is converted into lead carbonate in ammonium or sodium carbonate solution at 50-80°C followed by the separation of lead carbonate formed from the unconverted sulfide ores by flotation. Gold associated with sulfide ore (such as pyrite and chalcopyrite) can be extracted into sodium thiosulfate solution without any pretreatment such as roasting, high pressure aqueous oxidation or bacteria pre-leaching.
基金supported by the National Key Research and Development Project of China(2018YFC1903400)Key Research and Development Program of Jiangxi Province(20212BBG73049)+1 种基金Jiangxi Provincial Department of Education Science and Technology Research Project(GJJ190486)Excellent Doctoral Dissertation Cultivating Project of Jiangxi University of Science and Technology(202202400013)。
文摘Fluorinated rare earth molten-salt electrolytic slag contains a considerable amount of rare earth elements,as well as a variety of heavy metals and fluorides that cause environmental pollution.Therefore,it is of great importance to fully utilise this resource.In this study,the transformation mechanism of fluorinated rare earth molten-salt electrolytic slag roasted with sodium carbonate,and the regulation mechanism of rare earth leaching under different roasting conditions were investigated with the help of thermodynamic calculation of the reactions and kinetic analysis.The thermodynamic and differential thermal thermogravimetric(DTA-TG)analysis shows that the transformation of rare earth fluoride to rare earth oxide is promoted at elevated temperature.Furthermore,the leaching experimental results show that increasing the temperature,time,hydrochloric acid concentration,and liquid-solid ratio can effectively promote the recovery of rare earths.The optimum experimental conditions are a roasting temperature of 700℃,roasting time of 2 h,and sodium carbonate to molten salt electrolytic slag mass ratio of 0.6,followed by leaching at 80℃with a liquid-solid ratio of 10:1 by adding 3 moI/L hydrochlo ric acid with stirring for 2 h.Under these conditions,the rare earths in the molten salt electrolytic slag are biologically transformed at a lower temperature and the leaching efficiency of rare earths exceeds 98%.
文摘This paper critically reviewed the current knowledge and challenges of rice husk biochar(RHB)production and its effects on soil properties,plant growth,immobilization of heavy metals,reduction of nutrient leaching and mitigation of greenhouse gas emissions.The characteristics of RHBs produced at various pyrolysis temperatures were discussed and compared to biochars derived from other agro-industrial wastes.RHBs produced at higher pyrolysis temperatures show lower hydrogen/carbon ratio,which suggests the presence of higher aromatic carbon compounds.The increase of pyrolysis temperature also results in production of RHBs with higher ash content,lower yield and higher surface area.RHB usually has higher silicon and ash contents and lower carbon content compared to biochars derived from other feedstocks at the same pyrolysis conditions.Although it depends on soil type,RHB application can improve soil organic carbon content,cation exchange capacity,available K concentration,bulk density and microbial activity.The effect of RHB on soil aggregation mainly depends on soil texture.The growth of different crops is also enhanced by application of RHB.RHB addition to soil can immobilize heavy metals and herbicides and reduce their bioavailability.RHB application shows a significant capacity in reduction of nitrate leaching,although its magnitude depends on the biochar application rate and soil biogeochemical characteristics.Use of RHB,especially in paddy fields,shows a promising mitigation effect on greenhouse gas(CH4,CO2 and N2O)emissions.Although RHB characteristics are also related to other factors such as pyrolysis heating rate and residence time,its performance for specific applications(e.g.carbon sequestration,pH amendment)can be manipulated by adjusting the pyrolysis temperature.More research is needed on long-term field applications of RHB to fully understand the advantages and disadvantages of RHB as a soil amendment.
基金Project supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry of Chinathe United States-Israel Binational Agricultural Research and Development Fund (No.452420)the Program for Changjiang Scholars and Innovative Research Team in University, China (No.IRT0657)
文摘A laboratory lysimeter experiment was conducted to investigate the effects of forage corn (Zea mays L.) stalk application on the CO2 concentration in soil air and calcareous sodic soil reclamation. The experimental treatments tested were soil exchangeable sodium percentage (ESP) levels of 1, 11, and 19, added corn stalk contents of 0 to 36 g kg-1, and incubation durations of 30 and 60 days. The experimental results indicated that corn stalk application and incubation significantly increased CO2 partial pressure in soil profile and lowered pH value in soil solution, subsequently increased native CaCO3 mineral dissolution and electrolyte concentration of soil solution, and finally significantly contributed to reduction on soil sodicity level. The reclamation effciency of calcareous sodic soils increased with the added corn stalk. When corn stalks were added at the rates of 22 and 34 g kg-1 into the soil with initial ESP of 19, its ESP value was decreased by 56% and 78%, respectively, after incubation of 60 days and the leaching of 6.5 pore volumes (about 48 L of percolation water) with distilled water. Therefore, crop stalk application and incubation could be used as a choice to reclaim moderate calcareous sodic soils or as a supplement of phytoremediation to improve reclamation effciency.