Leaching kinetics of acid-soluble Cr（VI） in chromite ore processing residue （COPR） using hydrofluoric （HF） acid solution as a leaching agent was investigated for potential remediation of COPR with industrial was...Leaching kinetics of acid-soluble Cr（VI） in chromite ore processing residue （COPR） using hydrofluoric （HF） acid solution as a leaching agent was investigated for potential remediation of COPR with industrial waste water containing HF. The results show that HF can effectively destabilize the Cr（VI）-bearing minerals, resulting in the mobilization of Cr（VI） from COPR into the leachate. Particle size significantly influences the leaching of acid-soluble Cr（VI） from COPR, followed by leaching time, whereas the effects of HF concentration and leaching temperature are slight and the influence of stirring rate is negligible. The leaching process of acid-soluble Cr（VI） from COPR is controlled by the diffusion through the product layer. The apparent activation energy is 8.696 kJ/mol and the reaction orders with respect to HF concentration and particle size is 0.493 8 and -2.013 3, respectively.展开更多
In this paper, environmental scanning electron microscopy （ESEM） is applied to characterizing the mineral and element distribution of chromite ore processing residue （COPR）. The test results show that Cr-bearing b...In this paper, environmental scanning electron microscopy （ESEM） is applied to characterizing the mineral and element distribution of chromite ore processing residue （COPR）. The test results show that Cr-bearing brownmillerite occurs in the rim of COPR particle, while hydroandradite with Cr （Ⅵ） in its structure presents inside the COPR particle. Periclase and calcite occur in the interstitial area. Element analyses show that Ca, Fe and Al are distributed throughout the COPR particle, and Mg exists mostly in the interstitial area or on the particle surface. A lower content of Cr is evenly distributed in the COPR particle, while slightly higher concentration of Cr occurs inside the particle. It is suggested that it will take a relatively longer time for Cr to migrate out of COPR, especially fbr hexavalent chromium, so the leaching time and the particle size may be two important factors to affect the release of Cr （Ⅵ）.展开更多
Remediation of COPR sites requires the key information including chromium oxidation, speciation and spatial distribution. Samples were gathered from a COPR site in Luliang County in Qujing, Yunnan Province of China. T...Remediation of COPR sites requires the key information including chromium oxidation, speciation and spatial distribution. Samples were gathered from a COPR site in Luliang County in Qujing, Yunnan Province of China. The total Cr, Cr(VI) and chromium species were investigated. Results indicated the concentration of total Cr was between 110.5 and 21,774 mg/kg, and the concentration of Cr(VI) was between 0.1 and 1075 mg/kg. The map of total-Cr and ratio of Cr(VI)/total-Cr(%) showed that the maximum of total-Cr and Cr(VI) appeared in the layers near the surface. In the horizontal direction, the pollution was more serious in the middle and southeast part than that in the west. Additionally, acid extractable chromium increased in the layers at depth from-0.3 to-2.0 m, and it decreased in the deeper layers. There was a trend that the movable Cr(VI) migrated to the deeper layers, and then it turned into Cr(III). Water played an important role for the Cr distribution. Cr(VI) in COPR released to the soil solution after rainfall, and then gravity led the solution down to the deeper layers. After repeated rainfall and leaching,Cr(VI) moved to the deeper soil layers. Due to capillarity and evaporation, Cr(VI) migrated and was enriched at thesurface layer. Therefore, measures on controlling water movement should be taken in the remediation of the COPR site.展开更多
The effective extracting Cr(Ⅵ) from chromite ore processing residue(COPR) is the key to achieve COPR detoxification and recovery.We developed an effective method to extract Cr(Ⅵ) from COPR via controlling the phase ...The effective extracting Cr(Ⅵ) from chromite ore processing residue(COPR) is the key to achieve COPR detoxification and recovery.We developed an effective method to extract Cr(Ⅵ) from COPR via controlling the phase transformation of Cr(Ⅵ)-containing minerals.Characteristic analysis showed that Cr(Ⅵ) was mainly incorporated in the hydrocalumite(NaCa4Al2O6(SO4/CrO4)1.5-15H2O) in COPR,which was a layered-double hydroxide(LDH) with multilayer structure.In the hydrothermal treatment experiments,the Na2CO3 solution showed significant extraction effect of Cr(Ⅵ) and detoxification effect of COPR.After treatment,95% of Cr(Ⅵ) was removed and the Cr(Ⅵ) concentration in the leachate was decreased to 1.6 mg/L by the toxicity characteristic leaching procedure(TCLP),within the regulatory limit disposal standard(HJ/T 301-2007,3 mg/L).Further study revealed that,during the treatment,hydrocalumite transformed into calcite(CaCO3) under the effect of mineralizer,therefore,the layered structure collapsed and the incorporated Cr(Ⅵ) was released to the supernatant.Meanwhile,the Cr(Ⅵ)desorbed from calcite with the calcite particles grew into large size with smooth surface.Stir-flow experiment revealed that the amount of chromium released from CORP to the environment was significantly reduced after treatment,and it is safer for landfill disposal.This work will provide an instructive guidance for the detoxification and recovery of COPR.展开更多
As species we humans generate excessive amounts of waste and hence for sustainability we should explore innovative ways to recover them.The primary objective of this study is to demonstrate an efficient and optimum wa...As species we humans generate excessive amounts of waste and hence for sustainability we should explore innovative ways to recover them.The primary objective of this study is to demonstrate an efficient and optimum way to recover chromium and iron from chromite ore processing residues(COPR)for the production of chrome steel and stainless steel.In Hudson County,New Jersey,there are more than two million tons of leftover COPR.Part of COPR was used as fill materials for construction sites,which spread the problem to a larger area.With high solubility along with their toxicity leached chromate from COPR is threatening the environment as well as human health.In this research,COPR was thermally treated to recover iron with chromium by applying techniques used in steel manufacturing.An extensive experimental program was performed using a Thermo-Gravimetric Analyzer(TGA)and bench scale tests to thermally treat the processed chromium contaminated soils with carbon and sand at varying temperatures and under reducing environment.The optimum chemical composition of COPR and additives to be used in the melts were evaluated based upon the thermodynamic properties of the mixture to ensure good phase separation,least amounts of iron and chromium oxides in the slag and minimum variability of final product(steel or iron with chromium).The impact of other oxides on the steel making process was evaluated to minimize the adverse impact on the process.The research demonstrated the feasibility of recovering a valuable construction material(chrome steel)from a waste(COPR).展开更多
基金Project(2009FJ1009) supported by Major Program of Hunan Provincial Science and Technology, ChinaProject(2005CB6237) supported by the National Basic Research Program of China
文摘Leaching kinetics of acid-soluble Cr（VI） in chromite ore processing residue （COPR） using hydrofluoric （HF） acid solution as a leaching agent was investigated for potential remediation of COPR with industrial waste water containing HF. The results show that HF can effectively destabilize the Cr（VI）-bearing minerals, resulting in the mobilization of Cr（VI） from COPR into the leachate. Particle size significantly influences the leaching of acid-soluble Cr（VI） from COPR, followed by leaching time, whereas the effects of HF concentration and leaching temperature are slight and the influence of stirring rate is negligible. The leaching process of acid-soluble Cr（VI） from COPR is controlled by the diffusion through the product layer. The apparent activation energy is 8.696 kJ/mol and the reaction orders with respect to HF concentration and particle size is 0.493 8 and -2.013 3, respectively.
基金Supported by National Natural Science Foundation of China (No. 50808091)
文摘In this paper, environmental scanning electron microscopy （ESEM） is applied to characterizing the mineral and element distribution of chromite ore processing residue （COPR）. The test results show that Cr-bearing brownmillerite occurs in the rim of COPR particle, while hydroandradite with Cr （Ⅵ） in its structure presents inside the COPR particle. Periclase and calcite occur in the interstitial area. Element analyses show that Ca, Fe and Al are distributed throughout the COPR particle, and Mg exists mostly in the interstitial area or on the particle surface. A lower content of Cr is evenly distributed in the COPR particle, while slightly higher concentration of Cr occurs inside the particle. It is suggested that it will take a relatively longer time for Cr to migrate out of COPR, especially fbr hexavalent chromium, so the leaching time and the particle size may be two important factors to affect the release of Cr （Ⅵ）.
基金supported by the Shandong Provincial Natural Science Foundation,China(Grant No.ZR2013DM008)the National Research Foundation for the Doctoral Program of Higher Education of China(No.20113718110007 for tutors)
文摘Remediation of COPR sites requires the key information including chromium oxidation, speciation and spatial distribution. Samples were gathered from a COPR site in Luliang County in Qujing, Yunnan Province of China. The total Cr, Cr(VI) and chromium species were investigated. Results indicated the concentration of total Cr was between 110.5 and 21,774 mg/kg, and the concentration of Cr(VI) was between 0.1 and 1075 mg/kg. The map of total-Cr and ratio of Cr(VI)/total-Cr(%) showed that the maximum of total-Cr and Cr(VI) appeared in the layers near the surface. In the horizontal direction, the pollution was more serious in the middle and southeast part than that in the west. Additionally, acid extractable chromium increased in the layers at depth from-0.3 to-2.0 m, and it decreased in the deeper layers. There was a trend that the movable Cr(VI) migrated to the deeper layers, and then it turned into Cr(III). Water played an important role for the Cr distribution. Cr(VI) in COPR released to the soil solution after rainfall, and then gravity led the solution down to the deeper layers. After repeated rainfall and leaching,Cr(VI) moved to the deeper soil layers. Due to capillarity and evaporation, Cr(VI) migrated and was enriched at thesurface layer. Therefore, measures on controlling water movement should be taken in the remediation of the COPR site.
基金the National Natural Science Foundation of China(No.21836002)the Young Innovative Talents Project in Higher Education of Guangdong(No.2018KQNCX002)+3 种基金Guangdong Innovative and Entrepreneurial Research Team Program(No.2016ZT06N569)the Fundamental Research Funds for the Central Universities(No.D2192000)the Shaoguan Special Fund for Soil Pollution Prevention and Control(No.2017sgtyfz103)the Youth Talent Promotion Project of Guangzhou Science and Technology Association(No.X20200301029)。
文摘The effective extracting Cr(Ⅵ) from chromite ore processing residue(COPR) is the key to achieve COPR detoxification and recovery.We developed an effective method to extract Cr(Ⅵ) from COPR via controlling the phase transformation of Cr(Ⅵ)-containing minerals.Characteristic analysis showed that Cr(Ⅵ) was mainly incorporated in the hydrocalumite(NaCa4Al2O6(SO4/CrO4)1.5-15H2O) in COPR,which was a layered-double hydroxide(LDH) with multilayer structure.In the hydrothermal treatment experiments,the Na2CO3 solution showed significant extraction effect of Cr(Ⅵ) and detoxification effect of COPR.After treatment,95% of Cr(Ⅵ) was removed and the Cr(Ⅵ) concentration in the leachate was decreased to 1.6 mg/L by the toxicity characteristic leaching procedure(TCLP),within the regulatory limit disposal standard(HJ/T 301-2007,3 mg/L).Further study revealed that,during the treatment,hydrocalumite transformed into calcite(CaCO3) under the effect of mineralizer,therefore,the layered structure collapsed and the incorporated Cr(Ⅵ) was released to the supernatant.Meanwhile,the Cr(Ⅵ)desorbed from calcite with the calcite particles grew into large size with smooth surface.Stir-flow experiment revealed that the amount of chromium released from CORP to the environment was significantly reduced after treatment,and it is safer for landfill disposal.This work will provide an instructive guidance for the detoxification and recovery of COPR.
基金The work described in this study was supported by a research contract from the New Jersey Department of Environmental Protection.
文摘As species we humans generate excessive amounts of waste and hence for sustainability we should explore innovative ways to recover them.The primary objective of this study is to demonstrate an efficient and optimum way to recover chromium and iron from chromite ore processing residues(COPR)for the production of chrome steel and stainless steel.In Hudson County,New Jersey,there are more than two million tons of leftover COPR.Part of COPR was used as fill materials for construction sites,which spread the problem to a larger area.With high solubility along with their toxicity leached chromate from COPR is threatening the environment as well as human health.In this research,COPR was thermally treated to recover iron with chromium by applying techniques used in steel manufacturing.An extensive experimental program was performed using a Thermo-Gravimetric Analyzer(TGA)and bench scale tests to thermally treat the processed chromium contaminated soils with carbon and sand at varying temperatures and under reducing environment.The optimum chemical composition of COPR and additives to be used in the melts were evaluated based upon the thermodynamic properties of the mixture to ensure good phase separation,least amounts of iron and chromium oxides in the slag and minimum variability of final product(steel or iron with chromium).The impact of other oxides on the steel making process was evaluated to minimize the adverse impact on the process.The research demonstrated the feasibility of recovering a valuable construction material(chrome steel)from a waste(COPR).
