Red mud(RM) is an industrial solid waste produced during the extraction of alumina from bauxite.The strong alkaline and heavy metal leaching issues are the primary factors limiting its utilization.This paper proposes ...Red mud(RM) is an industrial solid waste produced during the extraction of alumina from bauxite.The strong alkaline and heavy metal leaching issues are the primary factors limiting its utilization.This paper proposes a method for dealkalization and chromium(Cr) removal by repeated freeze and thaw to enhance the comprehensive utilization rate of RM.This study focused on the Bayer RM and investigated the effects of freeze-thaw(FT)-acid washing(AW) for dealkalization and Cr removal.The variables were the eluent concentration and FT cycles.The results showed that the synergistic action of FT-AW significantly improved the efficiency of dealkalization and Cr removal.After five FT cycles with 0.5 mol/L oxalic acid,the dealkalization and Cr removal rates reached 97.5% and 65.38%,respectively,16.1% and 7.40% higher than those achieved at room temperature.The repeated FT disrupted the structure of the RM particles,leading to an increase in the pore space between the soil particles.This enables complete eluent contact and reaction with Cr and alkali,thereby enhancing the removal rate.The FT-AW process is suitable for practical engineering applications.It offers a novel method for RM dealkalization and Cr removal by using the FT alternation phenomena in seasonally frozen regions.展开更多
Bauxite residue,a byproduct of alumina manufacture,is a serious environmental pollutant due to its high leaching contents of metals and caustic compounds.Four typical anions of CO3^2-,HCO3^-,Al(OH)4^- and OH-(represen...Bauxite residue,a byproduct of alumina manufacture,is a serious environmental pollutant due to its high leaching contents of metals and caustic compounds.Four typical anions of CO3^2-,HCO3^-,Al(OH)4^- and OH-(represented caustic compounds) and metal ions(As,B,Mo and V) were selected to assess their leaching behavior under dealkalization process with different conditions including liquid/solid ratio(L/S ratio),temperature and leaching time.The results revealed that washing process could remove the soluble composition in bauxite residue effectively.The leaching concentrations of typical anions in bauxite residue decreased as follows:c(CO3^2-)> c(HCO3^-)> c[Al(OH)4-]> c(OH-).L/S ratio had a more significant effect on leaching behavior of OH-,whilst the leaching concentration of Al(OH)4-varied larger underleaching temperature and time treatment.Under the optimal leaching,the total alkaline,soluble Na concentrations,exchangeable Ca concentrations were 79.52,68.93,and 136.0 mmol/L,respectively,whilst the soluble and exchangeable content of As,B,Mo and V in bauxite residue changed slightly.However,it should be noted that water leaching has released metal ions such as As,B,Mo and V in bauxite residue to the surrounding environment.The semiquantitative analysis of XRD revealed that water leaching increased the content of gismondine from 2.4% to 6.4%.The SEM images demonstrated the dissolution of caustic compounds on bauxite residue surface.The correlation analysis indicated that CO3^2- and HCO3^- could effectively reflect the alkalinity of bauxite residue,and may be regarded as critical de alkalization indicators to evaluate alkalinity removal in bauxite residue.展开更多
基金supported by the National Natural Science Foundation of China (No. U2004181)State Key Laboratory of Frozen Soil Engineering (No. SKLFSE20191702)+2 种基金the key scientific and technological project of Henan Province (222102320226)Basic research expenses of Henan Polytechnic University (NSFRF230424)the Natural Science Foundation of Henan Province (242300421650)。
文摘Red mud(RM) is an industrial solid waste produced during the extraction of alumina from bauxite.The strong alkaline and heavy metal leaching issues are the primary factors limiting its utilization.This paper proposes a method for dealkalization and chromium(Cr) removal by repeated freeze and thaw to enhance the comprehensive utilization rate of RM.This study focused on the Bayer RM and investigated the effects of freeze-thaw(FT)-acid washing(AW) for dealkalization and Cr removal.The variables were the eluent concentration and FT cycles.The results showed that the synergistic action of FT-AW significantly improved the efficiency of dealkalization and Cr removal.After five FT cycles with 0.5 mol/L oxalic acid,the dealkalization and Cr removal rates reached 97.5% and 65.38%,respectively,16.1% and 7.40% higher than those achieved at room temperature.The repeated FT disrupted the structure of the RM particles,leading to an increase in the pore space between the soil particles.This enables complete eluent contact and reaction with Cr and alkali,thereby enhancing the removal rate.The FT-AW process is suitable for practical engineering applications.It offers a novel method for RM dealkalization and Cr removal by using the FT alternation phenomena in seasonally frozen regions.
基金supported by the National Natural Science Foundation of China(Nos.41701587,41877511)the Fundamental Research Funds for the Central Universities of Central South University(No.202045010)。
文摘Bauxite residue,a byproduct of alumina manufacture,is a serious environmental pollutant due to its high leaching contents of metals and caustic compounds.Four typical anions of CO3^2-,HCO3^-,Al(OH)4^- and OH-(represented caustic compounds) and metal ions(As,B,Mo and V) were selected to assess their leaching behavior under dealkalization process with different conditions including liquid/solid ratio(L/S ratio),temperature and leaching time.The results revealed that washing process could remove the soluble composition in bauxite residue effectively.The leaching concentrations of typical anions in bauxite residue decreased as follows:c(CO3^2-)> c(HCO3^-)> c[Al(OH)4-]> c(OH-).L/S ratio had a more significant effect on leaching behavior of OH-,whilst the leaching concentration of Al(OH)4-varied larger underleaching temperature and time treatment.Under the optimal leaching,the total alkaline,soluble Na concentrations,exchangeable Ca concentrations were 79.52,68.93,and 136.0 mmol/L,respectively,whilst the soluble and exchangeable content of As,B,Mo and V in bauxite residue changed slightly.However,it should be noted that water leaching has released metal ions such as As,B,Mo and V in bauxite residue to the surrounding environment.The semiquantitative analysis of XRD revealed that water leaching increased the content of gismondine from 2.4% to 6.4%.The SEM images demonstrated the dissolution of caustic compounds on bauxite residue surface.The correlation analysis indicated that CO3^2- and HCO3^- could effectively reflect the alkalinity of bauxite residue,and may be regarded as critical de alkalization indicators to evaluate alkalinity removal in bauxite residue.
