Effects Of Environmental Medium Ions On The Stability Of As(?)-Schwertmannite And Cr(?)-Jarosite During Aging

Acid Mine Drainage(AMD)usually has the characteristics of low pH,high heavy metal and high SO42-,which poses a great threat and damage to mine production and ecological environment.In this environment,large amount of hydroxyl sulfate iron minerals can be generated,such as schwertmannite and jarosite.Due to the high specific surface area and great adsorption capacity,schwertmannite and jarosite have a good fixation on heavy metals.Secondary iron minerals enriched with As,Cr and other pollutants were found in a large number of river sediments and soils in the mining area.However,with the change of environmental medium would produce dissolution or phase transformation,which could cause the release of As and Cr,resulting in environmental risks.Because of this,the stability of schwertmannite and jarosite is of great significance to the migration of heavy metals in solid and liquid phases.In order to explore the effect of environmental media on the phase transformation of As(?)-containing schwertmannite(As-Sch)and Cr(?)-containing jarosite(Cr-Jar)during aging,as well as the release law of as(?)and Cr(?),the following research is carried out in this paper.As-Sch and Cr-Jar were prepared by biological coprecipitation.For schwertmannite and jarosite,Cl',Cu2+and NO3-,Mn2+were selected as influencing factors,respectively,aging at EPS solution with initial pH 2 to simulate the real AMD environment for 180 days.The effects of cation and anion ions in environmental medium on mineral phase transformation and pollutant migration during iron mineral aging were explored.By monitoring the pH value,concentration of Fe3+,As(?)and Cr(?)in the solution during the aging process,and characterizing the aging products by XRD,FTIR and FESEM,the results are as follows:The As(?)-Sch would be completely converted into jarosite within 7 days,most of the fixed As(?)would be released,while only a small part of As(?)will be re-adsorbed by jarosite.The addition of Cl-forms Fe-Cl complex on the mineral surface,which makes the crystalliriity of the aging products lower and reduces the adsorption sites of As(?).High concentration of Cu2+would replace Fe(?)in the iron ore structure,resulting in the unstable iron ore structure and more release of As(?).Cl' and Cu2+could accelerate the formation rate of jarosite in the aging process.Spherical jarosite appears in the ore phase in 1-3 days,and then gradually grows into cubes.The mineral phase of Cr(?)-Jar remains stable during aging,and there is only the dissolution and regeneration of jarosite in the solution.The addition of NO3-greatly reduced the release of Cr(?),compared with the treatment without NO3-,the concentration of Cr(?)in the solution decreased by about 50%.The addition of Mn2+has great impact on the redistribution of Cr(?).The concentration of Cr(?)in the solution decreases in the early stage of aging process,but inhibits the adsorption of Cr(?)in the middle and late stage of aging.When the concentration of Cr(?)in the solution without Mn2+decreases,the concentration of Cr(?)in the solution with Mn2+still increases,and finally the concentration of Cr(?)in the solution increases by 30%?50%.NO3-has a destructive effect on jarosite,which intensifies the dissolution of jarosite and accelerates the dissolution generation cycle on the surface of jarosite.Finally,the size of the aggregates of aging products is smaller and the particle size on the mineral surface is more uniform.The above research results reveal the law of phase transformation,dissolution and pollutant release during the aging of As-Sch and Cr-Jar.It provides theoretical guidance for mine environmental risk assessment and mine environmental governance.