The precipitation of the water-leaching solution of Baotou mixed rare earth(RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewat...The precipitation of the water-leaching solution of Baotou mixed rare earth(RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewater because of the relatively low solubility of rare earth sulfate.To solve the serious problem of ammonia-nitrogen pollution,new precipitators need to be developed urgently so as to meet the requirements of environmental protection and impurities content of the product(SO_(4)^(2-)<1.8 wt% in RE carbonates products).In this paper,we studied the effects of feeding modes on the behavior of SO_(4)^(2-) during the preparation of light RE carbonate(RE=La,Ce,Pr,Nd) from their sulfate solutions using Mg(HCO_(3))_(2) as a precipitant.The results indicate that the contents of SO_(4)^(2-) in the La and Ce precipitates using positive feeding mode exceed 16 wt% because of the formation of La_(2)(CO_(3))2.15(-SO_(4))0.85·4 H_(2)O and Ce_(2)(CO_(3))_(2).15(SO_(4))0.85·3H_(2)O,while those of the Pr and Nd precipitates are 4 wt%-5 wt% since they exist in the form of n-carbonate.The precipitates prepared using synchronous feeding mode are all RE carbonate with only 4 wt%-5 wt% of SO_(4)^(2-) enclosed in the precipitation.The content of SO_(4)^(2-) in the RE carbonate obtained using reverse feeding mode is the lowest.Among them,the content of SO_(4)^(2-) in La precipitate is only 1.40 wt%.Both synchronous and reverse feeding modes can effectively reduce the content of SO_(4)^(2-)in RE carbonate,which provides theoretical guidance for the preparation of qualified light RE carbonate products by Mg(HCO3)2 precipitation method.展开更多
Per-and polyfluoroalkyl substances(PFASs)represent an increasingly global challenge for keeping water and soil“non-toxic”.100 of millions of people are exposed to PFAS levels of concern,in particular,around PFAS pro...Per-and polyfluoroalkyl substances(PFASs)represent an increasingly global challenge for keeping water and soil“non-toxic”.100 of millions of people are exposed to PFAS levels of concern,in particular,around PFAS production sites and sites where PFASs are/were used and released or disposed.The Stockholm Convention established recommendations to systematically assess PFOS pollution which can be transposed to all PFASs considering that PFASs are an issue of concern under The Strategic Approach to International Chemical Management(SAICM).One major wide-spread source of environmental pollution is the long-term use of PFAS-containing fire extinguishing agents.Strategies for the reduction of human exposure need to reduce and were feasible eliminate the current uses of PFASs and reduce and eliminate the human exposure from the contamination of the environment from past uses including contaminated drinking water.The current study shows that well-known methods of water treatment,especially the use of materials for adsorption and ion exchange,can often neither guarantee satisfactory cleaning results nor economically justifiable filter running times at high PFAS concentrations and complex matrix conditions.Their combination with a pre-precipitation stage using specialized precipitants can significantly optimize treatment successes.PFAS is still being released into the environment in considerable quantities by e.g.the use of so-called aqueous film forming foams(AFFF).Fire departments are increasingly trying to reduce the risks associated with the use of AFFF agents for the health of firefighting personnel and the environment by replacing AFFF foaming agents with fluorine-free foaming agents.If the fluorine-containing foaming agents are simply replaced,considerable residual PFAS loads often remain in the fire extinguishing systems contaminated with PFAS(fire engines,fire boats,stationary fire extinguishing systems,etc.),which are then discharged further into the environment during renewed operations-normally at a reduced concentration.The current study demonstrate that a conscientious decontamination of systems previously in contact with PFAS is therefore urgently required.Here,too,precipitants specialized for PFAS adsorption can make an important contribution to protecting the environment.Sites were firefighting equipment has been cleaned over years can also be considered contaminated and need assessment and possibly remediation.展开更多
Magnesium bicarbonate, prepared by the carbonation of magnesium hydroxide slurry, was used as a novel saponifier to eliminate the ammonia nitrogen pollution in the rare earth extraction separation process. The effect ...Magnesium bicarbonate, prepared by the carbonation of magnesium hydroxide slurry, was used as a novel saponifier to eliminate the ammonia nitrogen pollution in the rare earth extraction separation process. The effect of impurity ions introduced by system on the carbonation reaction of magnesium hydroxide was studied in the work. The results showed that the presence of Ca2＋could lead to side reactions so as to reduce the conversion rate of magnesium hydroxide, and a small number of rare earth ions would have great influence on the carbonation reaction. What’s more, there was no influence on carbonation reaction with the low concen-tration of Na＋or Mg2＋, the conversion rate of magnesium hydroxide could reach above 96%. This paper showed a practical theory which could provide scientific guidance for the preparation of novel saponifier in rare earth extraction separation process.展开更多
基金Project supported by the National Natural Science Foundation of China(51674037,51674036)Guangxi Science and Technology Major Project(Guike-AA18242022)。
文摘The precipitation of the water-leaching solution of Baotou mixed rare earth(RE) concentrate roasted with sulfuric acid using ammonium bicarbonate for producing RE carbonate produces a mass of ammonia-nitrogen wastewater because of the relatively low solubility of rare earth sulfate.To solve the serious problem of ammonia-nitrogen pollution,new precipitators need to be developed urgently so as to meet the requirements of environmental protection and impurities content of the product(SO_(4)^(2-)<1.8 wt% in RE carbonates products).In this paper,we studied the effects of feeding modes on the behavior of SO_(4)^(2-) during the preparation of light RE carbonate(RE=La,Ce,Pr,Nd) from their sulfate solutions using Mg(HCO_(3))_(2) as a precipitant.The results indicate that the contents of SO_(4)^(2-) in the La and Ce precipitates using positive feeding mode exceed 16 wt% because of the formation of La_(2)(CO_(3))2.15(-SO_(4))0.85·4 H_(2)O and Ce_(2)(CO_(3))_(2).15(SO_(4))0.85·3H_(2)O,while those of the Pr and Nd precipitates are 4 wt%-5 wt% since they exist in the form of n-carbonate.The precipitates prepared using synchronous feeding mode are all RE carbonate with only 4 wt%-5 wt% of SO_(4)^(2-) enclosed in the precipitation.The content of SO_(4)^(2-) in the RE carbonate obtained using reverse feeding mode is the lowest.Among them,the content of SO_(4)^(2-) in La precipitate is only 1.40 wt%.Both synchronous and reverse feeding modes can effectively reduce the content of SO_(4)^(2-)in RE carbonate,which provides theoretical guidance for the preparation of qualified light RE carbonate products by Mg(HCO3)2 precipitation method.
文摘Per-and polyfluoroalkyl substances(PFASs)represent an increasingly global challenge for keeping water and soil“non-toxic”.100 of millions of people are exposed to PFAS levels of concern,in particular,around PFAS production sites and sites where PFASs are/were used and released or disposed.The Stockholm Convention established recommendations to systematically assess PFOS pollution which can be transposed to all PFASs considering that PFASs are an issue of concern under The Strategic Approach to International Chemical Management(SAICM).One major wide-spread source of environmental pollution is the long-term use of PFAS-containing fire extinguishing agents.Strategies for the reduction of human exposure need to reduce and were feasible eliminate the current uses of PFASs and reduce and eliminate the human exposure from the contamination of the environment from past uses including contaminated drinking water.The current study shows that well-known methods of water treatment,especially the use of materials for adsorption and ion exchange,can often neither guarantee satisfactory cleaning results nor economically justifiable filter running times at high PFAS concentrations and complex matrix conditions.Their combination with a pre-precipitation stage using specialized precipitants can significantly optimize treatment successes.PFAS is still being released into the environment in considerable quantities by e.g.the use of so-called aqueous film forming foams(AFFF).Fire departments are increasingly trying to reduce the risks associated with the use of AFFF agents for the health of firefighting personnel and the environment by replacing AFFF foaming agents with fluorine-free foaming agents.If the fluorine-containing foaming agents are simply replaced,considerable residual PFAS loads often remain in the fire extinguishing systems contaminated with PFAS(fire engines,fire boats,stationary fire extinguishing systems,etc.),which are then discharged further into the environment during renewed operations-normally at a reduced concentration.The current study demonstrate that a conscientious decontamination of systems previously in contact with PFAS is therefore urgently required.Here,too,precipitants specialized for PFAS adsorption can make an important contribution to protecting the environment.Sites were firefighting equipment has been cleaned over years can also be considered contaminated and need assessment and possibly remediation.
基金Project supported by Key Program of National Natural Science Foundation of China(50934004)National High Technology Research and Development Program of China(2010AA03A405)National Science and Technology Support Program of China(2012BAE01B02)
文摘Magnesium bicarbonate, prepared by the carbonation of magnesium hydroxide slurry, was used as a novel saponifier to eliminate the ammonia nitrogen pollution in the rare earth extraction separation process. The effect of impurity ions introduced by system on the carbonation reaction of magnesium hydroxide was studied in the work. The results showed that the presence of Ca2＋could lead to side reactions so as to reduce the conversion rate of magnesium hydroxide, and a small number of rare earth ions would have great influence on the carbonation reaction. What’s more, there was no influence on carbonation reaction with the low concen-tration of Na＋or Mg2＋, the conversion rate of magnesium hydroxide could reach above 96%. This paper showed a practical theory which could provide scientific guidance for the preparation of novel saponifier in rare earth extraction separation process.
