Adsorption Characteristics And Mechanism Of Arsenic,Antimony,Lead And Cadmium By HCO-（Fe₃O₄）_x

"Antimony capital of the world"Hunan Lengshuijiang antimony mine,long-term high-intensity mining leads to the deterioration of the ecological environment of the mining area,heavy metal complex pollution in the soil and water environment is extremely serious.In consideration of the problem of heavy metal pollution in water,a variety of treatment methods have been studied and applied in practice,among which the adsorption method has received widely concerned,but abundant studies are limited to the simulation of heavy metal wastewater,and there is still a lack of research on the actual mining wastewater.In this study,the research group used HCO-（Fe₃O₄）_x adsorbent made of grinding and polishing sludge rich in hydrated cerium oxide（Ce O₂·H₂O abbreviated as HCO）to treat the mine wastewater,namely,the adsorption removal of antimony,arsenic,plumbum and cadmium in the actual wastewater water carried out a series of experimental studies.Test the actual waste water;Through static adsorption experiments,the influencing factors of Adsorption removal of As（Ⅴ）,Sb（Ⅴ）,Pb（Ⅱ）and Cd（Ⅱ）by HCO-（Fe₃O₄）_x adsorbent were investigated to study its adsorption performance.The selective adsorption of As（Ⅴ）,Sb（Ⅴ）,Pb（Ⅱ）and Cd（Ⅱ）in mixed system by HCO-（Fe₃O₄）_x adsorbent was investigated,which was applied in practice.The adsorption isothermal model and adsorption kinetic model were fitted to explore the adsorption process.The adsorbents before and after adsorption were analyzed by modern characterization techniques,so as to analyze the adsorption mechanism.（1）Analysis of water quality characteristics in Antimony mining area of Xikuang Mine.The analysis shows that the main parameters of wastewater are as follows:p H 6.8,COD=32 mg/L;The measured concentrations of arsenic,antimony,lead and cadmium are 0.53mg/L,2.95 mg/L,1.22 mg/L and 0.17 mg/L,respectively,and the heavy metals mainly exist in the wastewater in the valence form of As（Ⅴ）,Sb（Ⅴ）,Pb（Ⅱ）and Cd（Ⅱ）.And the main associated anions in the wastewater are NO₃^-,Cl^-,SO₄^2-,PO₄^3-,and Si O₃^2-.It can be seen that the actual antimony ore wastewater has the characteristics of multi-metal composite pollution（2）Influencing factors of Adsorption removal of As（Ⅴ）,Sb（Ⅴ）,Pb（Ⅱ）and Cd（Ⅱ）in a single system by HCO-（Fe₃O₄）_x adsorbent.The results show that the optimal conditions for removing As（Ⅴ）,Sb（Ⅴ）,Pb（Ⅱ）and Cd（Ⅱ）by HCO-（Fe₃O₄）_x adsorbent are as follows:p H=2～6,Fe/Ce molar ratio=1:1.5,adsorption equilibrium time=4 h,temperature 30℃,dosage2.0 g/L,respectively.p H=2～3,Fe/Ce molar ratio=1:1,adsorption equilibrium time=6 h,temperature 30℃,dosage 2.0 g/L;p H=4～5,Fe/Ce molar ratio=1:1.5,adsorption equilibrium time=4 h,temperature 30℃,dosage 2.0 g/L;p H=7～8,Fe/Ce molar ratio=1:1.5,adsorption equilibrium time=6 h,temperature 30℃,dosage 2.0 g/L。（3）Adsorption/desorption of As（Ⅴ）,Sb（Ⅴ）,Pb（Ⅱ）and Cd（Ⅱ）by HCO-（Fe₃O₄）_x.The results showed that among the four eluents,Na OH solution had the best elution effect.The adsorption and desorption of As（Ⅴ）and Pb（Ⅱ）for 5 times and Sb（Ⅴ）for 3 times can maintain the removal rate of more than 70%,indicating that HCO-（Fe₃O₄）_x has good regeneration potential.（4）The selective adsorption of As（Ⅴ）,Sb（Ⅴ）,Pb（Ⅱ）and Cd（Ⅱ）by HCO-（Fe₃O₄）_xwas studied.The results show that different p H have different effects on the adsorption of HCO-（Fe₃O₄）_x adsorbent.The priority order of HCO-（Fe₃O₄）_x adsorbent is As（Ⅴ）>Sb（Ⅴ）>Pb（Ⅱ）>Cd（Ⅱ）under acidic conditions,and that of Pb（Ⅱ）>As（Ⅴ）>Cd（Ⅱ）>Sb（Ⅱ）under alkaline conditions.Coexisting anions in water,such as Cl^-,SO₄^2-,PO₄^3-and Si O₃^2-,compete or promote adsorption.When HCO-（Fe₃O₄）_x adsorbent is applied to the actual wastewater,the adsorption capacity of HCO-（Fe₃O₄）_x adsorbent to the four pollutants can reach the discharge standard,and the adsorption capacity of As（Ⅴ）and Pb（Ⅱ）in the wastewater can reach the surface water standard.（5）Removal of arsenic,antimony,lead and cadmium by adsorption of HCO-（Fe₃O₄）_xadsorbent characterization,adsorption model fitting and analysis mechanism.The results show that Freundlich isothermal adsorption model and two kinetic models can describe the adsorption process well,indicating that the adsorption is multilayer adsorption based on chemical reaction.The maximum adsorption capacities of As（Ⅴ）,Sb（Ⅴ）and Pb（Ⅱ）at 30℃are 33.18 mg/g,46.00 mg/g,35.93 mg/g and 19.20 mg/g,respectively.Through characterization analysis,it is inferred that in the process of adsorption and removal of these four pollutants,Fe/Ce oxides and hydroxyl groups play a great role,mainly ligand exchange reaction,complexation reaction,surface precipitation,electrostatic adsorption,so as to transfer them from water to adsorbent.