This study focused on leaching behavior of alkaline anion and sodium in bauxite residue through ammonium chloride treatment.The results showed that the pH of bauxite residue decreased from 10.49 to 8.93,total alkaline...This study focused on leaching behavior of alkaline anion and sodium in bauxite residue through ammonium chloride treatment.The results showed that the pH of bauxite residue decreased from 10.49 to 8.93,total alkaline anion(HCO3^-,CO3^2-,OH^-,AlO2^-)concentration reduced from 38.89 to 25.50 mmol/L,leaching rate of soluble sodium was 80.86%with ammonium chloride addition of 0.75%,liquid/solid(L/S)ratio of 3(mL/g),temperature of 30°C and reaction time of 18 h;L/S ratio was the main factor affecting the removal of alkaline anion and the leaching of sodium.Furthermore,ammonium chloride promoted the dissolution of diaspore and changed the micro/morphological characteristics with the increase of massive structure.The findings of this work will contribute to achieve soil-formation of bauxite residue.展开更多
Aiming at alkaline problem of bauxite residue,this work focused variation of alkaline characteristics in bauxite residue through phosphogypsum treatment.The results demonstrated that the pH of bauxite residue reduced ...Aiming at alkaline problem of bauxite residue,this work focused variation of alkaline characteristics in bauxite residue through phosphogypsum treatment.The results demonstrated that the pH of bauxite residue reduced from initial 10.83 to 8.70 when 1.50 wt%phosphogypsum was added for 91 d.The removal rates of free alkali and exchangeable sodium were 97.94%and 75.87%,respectively.Meanwhile,significant positive correlations(P<0.05)existed between pH and free alkali,exchangeable sodium.The effect of free alkali composition was CO3^2–>OH^–>AlO2^–>HCO3^–.In addition,alkaline phase decreased from 52.81%to 48.58%and gypsum stably presented in bauxite residue which continuously provided Ca^2+to inhibit dissolution of combined alkali.Furthermore,phosphogypsum promoted formation of macroaggregate structure,increased Ca^2+,decreased Na+and Al^3+on the surface of bauxite residue significantly,ultimately promoting soil formation in bauxite residue.展开更多
A novel integrated approach to remove the free alkalis and stabilize solid-phase alkalinity by controlling the release of Ca from desulfurization gypsum was developed.The combination of recycled FeCl_(3)solution and E...A novel integrated approach to remove the free alkalis and stabilize solid-phase alkalinity by controlling the release of Ca from desulfurization gypsum was developed.The combination of recycled FeCl_(3)solution and EDTA activated desulfurization gypsum lowered the bauxite residue pH to 7.20.Moreover,it also improved the residual Ca state,with its contribution to the total exchangeable cations increased(68%-92%).Notably,the slow release of exchangeable Ca introduced through modified desulfurization gypsum induced a phase transition of the alkaline minerals.This treatment stabilized the dealkalization effect of bauxite residue via reducing its overall acid neutralization capacity in abating pH rebound.Hence,this approach can provide guidance for effectively utilizing desulfurization gypsum to achieve stable regulation of alkalinity in bauxite residue.展开更多
Reduction of the high alkalinity of bauxite residue is a key problem to solve to make it suitable for plant growth and comprehensive utilization. In this study, phosphogypsum, a waste product from the phosphate fertil...Reduction of the high alkalinity of bauxite residue is a key problem to solve to make it suitable for plant growth and comprehensive utilization. In this study, phosphogypsum, a waste product from the phosphate fertilizer industry, was used to drive the alkaline transformation of the bauxite residue. Under optimal water washing conditions(liquid/solid ratio of 2 mL/g, 30°C, 24 hr), the impact of quantity added, reaction time and reaction mechanism during phosphogypsum application were investigated. Phosphogypsum addition effectively lowered p H levels and reduced the soluble alkalinity by 92.2%. It was found that the concentration of soluble Na and Ca ions in the supernatant increased gradually, whilst the exchangeable Na+and Ca^(2+)in solid phase changed 112 mg/kg and 259 mg/kg, respectively. Ca^(2+)became the dominant element in the solid phase(phosphogypsum addition of 2%, liquid/solid ratio of 2 mL/g, 30°C, 12 hr). X-ray diffraction data indicated that cancrinite and hydrogarnet were the primary alkaline minerals. SEM images suggested that phosphogypsum could promote the formation of stable macroaggregates, whilst the content of Ca^(2+)increased from 5.6% to 18.2% and Na reduced from 6.8% to 2.4%. Treatment with phosphogypsum could significantly promote the transformation of alkalinity cations by neutralization, precipitation and replacement reactions.This research provided a feasible method to promote soil formation of bauxite residue by phosphogypsum amendment.展开更多
This study revealed the relationship between the presence of calcium impurities and ammoniacal nitrogen concentration upon crystallization of struvite.The research hypothesis was that the presence of both calcium and ...This study revealed the relationship between the presence of calcium impurities and ammoniacal nitrogen concentration upon crystallization of struvite.The research hypothesis was that the presence of both calcium and high concentrations of ammoniacal nitrogen(328–1000 mg/L)in waste activated sludge may influence the struvite quality and acid stability.Hence,we studied the impact of Ca:Mg ratio upon morphology,particle size,purity and dissolution of struvite,in the presence of varying levels of excess ammoniacal nitrogen.X-ray diffraction revealed that up to 31.4%amorphous material was made which was assigned to hydroxyapatite.Increasing the ammoniacal nitrogen concentration and elevation of the Mg:Ca ratio maximized the presence of struvite.Struvite particle size was also increased by ammoniacal nitrogen as was twinning of the crystals.Tests with dilute solutions of organic acid revealed the sensitivity of struvite dissolution to the physical characteristics of the struvite.Smaller particles(21.2μm)dissolved at higher rates than larger particles(35.86μm).However,struvite dissolved rapidly as the p H was further reduced irrespective of the physical characteristics.Therefore,addition of struvite to low p H soils was not viewed as beneficial in terms of controlled nutrient release.Overall,this study revealed that waste activated sludge effluent with high ammoniacal nitrogen was prospective for synthesis of high quality struvite material.展开更多
Generation of alum sludge(AS)at drinking water treatment plants represents an environmental liability and adds to the cost of water purification.Consequently,this study explored the feasibility of using low and high c...Generation of alum sludge(AS)at drinking water treatment plants represents an environmental liability and adds to the cost of water purification.Consequently,this study explored the feasibility of using low and high carbon containing alum sludge from two water treatment plants to synthesize zeolite LTA.The hypothesis was that zeolite LTA synthesis was dependant upon alum sludge source and that a range of strategies may be required to optimize zeolite crystallinity.Zeolite characteristics such as morphology,phase composition,crystallinity,and particle size distribution were recorded."One pot"hydrothermal synthesis of precursor gel with molar composition 4.2 Na2O:Al2O3:1.2 SiO_(2):168 H2O at 80℃ for 3 hr resulted in 25 and 46 wt.%zeolite LTA from high and low carbonaceous sludge,respectively.Prior to hydrothermal reaction stage it was discovered that ageing of the gel,addition of zeolite LTA seeds,ultrasonic treatment and calcination all promoted zeolite LTA formation.Calcination of the alum sludge at 700℃ for 2 hr before hydrothermal synthesis resulted in particle size reduction and the highest amount of crystalline zeolite LTA:79 wt.%from low carbon sludge and 65 wt.%from high carbon sludge.Notably,the zeolite crystallinity reported in this study was the higher than previous studies on this topic.The outlined approach may allow value adding of alum waste and produce a commodity which could be used locally by the water treatment plant as a water softener.展开更多
Few studies have been carried out to connect nutrient recovery as struvite from wastewater and sustainable utilization of the recovered struvite for copper and zinc immobilization in contaminated soil.This study revea...Few studies have been carried out to connect nutrient recovery as struvite from wastewater and sustainable utilization of the recovered struvite for copper and zinc immobilization in contaminated soil.This study revealed the effect of struvite on Cu and Zn immobilization in contaminated bio-retention soil in the presence of commonly exuded plant organic acids.The research hypothesis was that the presence of both struvite and organic acids may influence the immobilization of Cu and Zn in soil.The outcome of this research confirmed that more than 99%of Cu and Zn was immobilized in bio-retention filter media by struvite application.Water-soluble Cu and Zn concentrations of struvite treated soil were less than 1.83 and 0.86 mg/kg respectively,and these concentrations were significantly lower compared to the total Cu and Zn content of 747.05 mg/kg in the contaminated soil.Application of struvite to Cu-and Zn-contaminated soil resulted in formation of compounds similar to zinc phosphate tetrahydrate(Zn3(PO4)2·4H2O)and amorphous Cu and Zn phases.Struvite was effective in heavy metal remediation in acidic soil regardless of the presence of Ca impurities in struvite and the presence of plant organic acids in soil.Overall,this study revealed that struvite recovered from wastewater treatment plants has potential for use as an amendment for heavy metal remediation in contaminated bio-retention soil.展开更多
基金Projects(41877511,41842020) supported by the National Natural Science Foundation of ChinaProject(201509048) supported by the Environmental Protection’s Special Scientific Research for Chinese Public Welfare Industry
文摘This study focused on leaching behavior of alkaline anion and sodium in bauxite residue through ammonium chloride treatment.The results showed that the pH of bauxite residue decreased from 10.49 to 8.93,total alkaline anion(HCO3^-,CO3^2-,OH^-,AlO2^-)concentration reduced from 38.89 to 25.50 mmol/L,leaching rate of soluble sodium was 80.86%with ammonium chloride addition of 0.75%,liquid/solid(L/S)ratio of 3(mL/g),temperature of 30°C and reaction time of 18 h;L/S ratio was the main factor affecting the removal of alkaline anion and the leaching of sodium.Furthermore,ammonium chloride promoted the dissolution of diaspore and changed the micro/morphological characteristics with the increase of massive structure.The findings of this work will contribute to achieve soil-formation of bauxite residue.
基金Projects(41877511,41842020)supported by the National Natural Science Foundation of China
文摘Aiming at alkaline problem of bauxite residue,this work focused variation of alkaline characteristics in bauxite residue through phosphogypsum treatment.The results demonstrated that the pH of bauxite residue reduced from initial 10.83 to 8.70 when 1.50 wt%phosphogypsum was added for 91 d.The removal rates of free alkali and exchangeable sodium were 97.94%and 75.87%,respectively.Meanwhile,significant positive correlations(P<0.05)existed between pH and free alkali,exchangeable sodium.The effect of free alkali composition was CO3^2–>OH^–>AlO2^–>HCO3^–.In addition,alkaline phase decreased from 52.81%to 48.58%and gypsum stably presented in bauxite residue which continuously provided Ca^2+to inhibit dissolution of combined alkali.Furthermore,phosphogypsum promoted formation of macroaggregate structure,increased Ca^2+,decreased Na+and Al^3+on the surface of bauxite residue significantly,ultimately promoting soil formation in bauxite residue.
基金supported by the National Natural Science Foundation of China(No.42307521)the China Postdoctoral Science Foundation(No.2023M742934)。
文摘A novel integrated approach to remove the free alkalis and stabilize solid-phase alkalinity by controlling the release of Ca from desulfurization gypsum was developed.The combination of recycled FeCl_(3)solution and EDTA activated desulfurization gypsum lowered the bauxite residue pH to 7.20.Moreover,it also improved the residual Ca state,with its contribution to the total exchangeable cations increased(68%-92%).Notably,the slow release of exchangeable Ca introduced through modified desulfurization gypsum induced a phase transition of the alkaline minerals.This treatment stabilized the dealkalization effect of bauxite residue via reducing its overall acid neutralization capacity in abating pH rebound.Hence,this approach can provide guidance for effectively utilizing desulfurization gypsum to achieve stable regulation of alkalinity in bauxite residue.
基金supported by the National Natural Science Foundation of China(Nos.41701587 and 41371475)the Environmental Protection's Special Scientific Research for Chinese Public Welfare Industry(No.201509048)
文摘Reduction of the high alkalinity of bauxite residue is a key problem to solve to make it suitable for plant growth and comprehensive utilization. In this study, phosphogypsum, a waste product from the phosphate fertilizer industry, was used to drive the alkaline transformation of the bauxite residue. Under optimal water washing conditions(liquid/solid ratio of 2 mL/g, 30°C, 24 hr), the impact of quantity added, reaction time and reaction mechanism during phosphogypsum application were investigated. Phosphogypsum addition effectively lowered p H levels and reduced the soluble alkalinity by 92.2%. It was found that the concentration of soluble Na and Ca ions in the supernatant increased gradually, whilst the exchangeable Na+and Ca^(2+)in solid phase changed 112 mg/kg and 259 mg/kg, respectively. Ca^(2+)became the dominant element in the solid phase(phosphogypsum addition of 2%, liquid/solid ratio of 2 mL/g, 30°C, 12 hr). X-ray diffraction data indicated that cancrinite and hydrogarnet were the primary alkaline minerals. SEM images suggested that phosphogypsum could promote the formation of stable macroaggregates, whilst the content of Ca^(2+)increased from 5.6% to 18.2% and Na reduced from 6.8% to 2.4%. Treatment with phosphogypsum could significantly promote the transformation of alkalinity cations by neutralization, precipitation and replacement reactions.This research provided a feasible method to promote soil formation of bauxite residue by phosphogypsum amendment.
基金funded through the financial support of “Australian Government Research Training Program (RTP) Stipend”supported by generous funding from the Science and Engineering Faculty (SEF-QUT)
文摘This study revealed the relationship between the presence of calcium impurities and ammoniacal nitrogen concentration upon crystallization of struvite.The research hypothesis was that the presence of both calcium and high concentrations of ammoniacal nitrogen(328–1000 mg/L)in waste activated sludge may influence the struvite quality and acid stability.Hence,we studied the impact of Ca:Mg ratio upon morphology,particle size,purity and dissolution of struvite,in the presence of varying levels of excess ammoniacal nitrogen.X-ray diffraction revealed that up to 31.4%amorphous material was made which was assigned to hydroxyapatite.Increasing the ammoniacal nitrogen concentration and elevation of the Mg:Ca ratio maximized the presence of struvite.Struvite particle size was also increased by ammoniacal nitrogen as was twinning of the crystals.Tests with dilute solutions of organic acid revealed the sensitivity of struvite dissolution to the physical characteristics of the struvite.Smaller particles(21.2μm)dissolved at higher rates than larger particles(35.86μm).However,struvite dissolved rapidly as the p H was further reduced irrespective of the physical characteristics.Therefore,addition of struvite to low p H soils was not viewed as beneficial in terms of controlled nutrient release.Overall,this study revealed that waste activated sludge effluent with high ammoniacal nitrogen was prospective for synthesis of high quality struvite material.
文摘Generation of alum sludge(AS)at drinking water treatment plants represents an environmental liability and adds to the cost of water purification.Consequently,this study explored the feasibility of using low and high carbon containing alum sludge from two water treatment plants to synthesize zeolite LTA.The hypothesis was that zeolite LTA synthesis was dependant upon alum sludge source and that a range of strategies may be required to optimize zeolite crystallinity.Zeolite characteristics such as morphology,phase composition,crystallinity,and particle size distribution were recorded."One pot"hydrothermal synthesis of precursor gel with molar composition 4.2 Na2O:Al2O3:1.2 SiO_(2):168 H2O at 80℃ for 3 hr resulted in 25 and 46 wt.%zeolite LTA from high and low carbonaceous sludge,respectively.Prior to hydrothermal reaction stage it was discovered that ageing of the gel,addition of zeolite LTA seeds,ultrasonic treatment and calcination all promoted zeolite LTA formation.Calcination of the alum sludge at 700℃ for 2 hr before hydrothermal synthesis resulted in particle size reduction and the highest amount of crystalline zeolite LTA:79 wt.%from low carbon sludge and 65 wt.%from high carbon sludge.Notably,the zeolite crystallinity reported in this study was the higher than previous studies on this topic.The outlined approach may allow value adding of alum waste and produce a commodity which could be used locally by the water treatment plant as a water softener.
基金River Sands Pty Ltd.,Australia for providing the bioretention filter material for this experiment and for their supportfunded through the financial support of“Australian Government Research Training Program(RTP)Stipend”supported by generous funding from the Science and Engineer-ing Faculty(QUT)。
文摘Few studies have been carried out to connect nutrient recovery as struvite from wastewater and sustainable utilization of the recovered struvite for copper and zinc immobilization in contaminated soil.This study revealed the effect of struvite on Cu and Zn immobilization in contaminated bio-retention soil in the presence of commonly exuded plant organic acids.The research hypothesis was that the presence of both struvite and organic acids may influence the immobilization of Cu and Zn in soil.The outcome of this research confirmed that more than 99%of Cu and Zn was immobilized in bio-retention filter media by struvite application.Water-soluble Cu and Zn concentrations of struvite treated soil were less than 1.83 and 0.86 mg/kg respectively,and these concentrations were significantly lower compared to the total Cu and Zn content of 747.05 mg/kg in the contaminated soil.Application of struvite to Cu-and Zn-contaminated soil resulted in formation of compounds similar to zinc phosphate tetrahydrate(Zn3(PO4)2·4H2O)and amorphous Cu and Zn phases.Struvite was effective in heavy metal remediation in acidic soil regardless of the presence of Ca impurities in struvite and the presence of plant organic acids in soil.Overall,this study revealed that struvite recovered from wastewater treatment plants has potential for use as an amendment for heavy metal remediation in contaminated bio-retention soil.
