The Treatment Of Arsenic-bearing Lime-ferrate Sludge And Arsenic-containing Wastewater Based On Crystal Phase Control Of Johnbaumite

Arsenic,called one of“five poisons element”,has attracted great attention in the world because of its widespread distribution and harmful.Arsenic-containing pollutants released by non-ferrous smelters account for 50.2%of total arsenic pollution emissions,which is the main source of arsenic pollution.Arsenic-bearing lime-ferrate sludge and high-concentration arsenic-containing wastewater are two typical arsenic-containing wastes in smelters.However,the existing treatment technology has obvious shortcomings:（1）The long-term stability of arsenic-bearing lime-ferrate sludge treated by traditional solidification/stabilization is not clear,resulting in arsenic may be released into the environment again under the environment and cause water and soil pollution;（2）Chemical precipitation methods such as the lime-iron salt method and sulfuration method can treat high-concentration arsenic-containing wastewater but the arsenic precipitates obtained are unstable and will form new arsenic pollution sources.Johnbaumite is a kind of arsenic-containing mineral with a high steady-state,which can exist in nature for a long time and is an ideal stabilization product.Its Ksp is very low(about 10^-40),which is beneficial to the deep removal of high-concentration arsenic.In this paper,we analyze the occurrence of arsenic in arsenic-bearing lime-ferrate sludge and proposed a zero-valent iron-enhanced hydrothermal method to stabilize arsenic in form of Johnbaumite.On the source treatment of arsenic pollution,arsenic-bearing gypsum,a typical industrial hazardous waste,was used as a treatment agent for high-concentration（10000 mg/L）arsenic-containing wastewater,and the arsenic-free supernatant and arsenic precipitation product Johnbaumite were obtained,thus realizing the dual treatment of arsenic-containing hazardous waste and wastewater.The main research contents and innovation points are as follows:（1）For arsenic-bearing lime-ferrate sludge,we firstly identified the unstable form of arsenic mainly combined with 2-line ferrihydrite.Based on this,ZVI-hydrothermal was developed as a new treatment for arsenic-bearing lime-ferrate sludge to complete the transformation of Johnbaumit.Under the optimum treatment conditions,the arsenic leaching concentration of product was decreased from 85.0 mg/L for untreated arsenic-bearing lime-ferrate sludge to 0.18 mg/L.Combined with XRD,FTIR,TEM,we systematically analyzed the phase composition,micro-morphology and arsenic speciation of samples.Furthermore,the mechanism of stabilizing arsenic by ZVI-hydrothermal was obtained.The arsenic stabilization involves three steps:（i）ZVI-mediated reaction with arsenic-laden 2-line Fh leading to the release of arsenate ions,（ii）hydrothermally facilitated phase transformation of gypsum causing the release of calcium ions,and（iii）formation and crystal growth of Johnbaumite.（2）Arsenic-containing gypsum was used as a reagent to remove arsenic from high-concentration arsenic-containing wastewater（10000 mg/L）.Under the optimum treatment conditions,the arsenic concentration in the solution will be reduced from the original 10000 to 0.22 mg/L,and the arsenic precipitation product of Johnbaumite will be obtained.The mechanism of arsenic-bearing gypsum in treating arsenic-containing wastewater was obtained by systematically analyzing the phase composition,microscopic morphology and arsenic occurrence.The process of removing arsenic from wastewater by arsenic-bearing gypsum to obtain stable Johnbaumite could be summarized as follows:（1）dissolution of arsenic-doped gypsum leading to the release of hydrogen arsenate ions,（2）hydrogen arsenate is converted into arsenate in an alkaline environment,（3）Johnbaumite precipitates from the solution.In this work,the double treatment of arsenic-containing hazardous waste and arsenic-containing wastewater was realized,and the secondary pollution of arsenic was avoided.