The Study On Arsenic Speciation Dynamics And Mechanisms In The Arsenic Tailings From Hunan Shimen Realgar Mine

In recent years,arsenic(As)pollution has caused worldwide concern.A large amount of arsenical tailing wastes were accumulated due to long-term mining activities.In the multipile effect of weathering,rainwater leaching,and geological microorganisms,a huge amount of As was activated and released,which cause a serious contamination to the mining area and the surrounding region and even pose a huge threat to human health.The oxidative/reductive dissolution of arsenic minerals mediated by microbes is an important process to influence the As behavior,which might cause serious As pollution in mining areas.Therefore,the As cycle due to the interaction between arsenic-bearing minerals and microbes and its environment influence need to be urgently studied.The As redox change driven by microbe is an important factor to influence its toxicity and mobility.However,most previous studies just focusd on the As speciation and release mechanism between the synthetic arsenic minerals and microbes.Besides,comparative studies on the As environment behavior in different types of arsenic tailings,microbial solid-liquid interactions,and other non-biological factors are still relatively little studied.Therefore,this paper firstly investigated the arsenic tailings types in Shimen Realgar Mine,Hunan.Then the As behavior and its environment effects in the tailings through anaerobic/aerobic miscrocom experiments were also investigated.A multidisciplinary theoretical knowledge of Mineralogy,Environmental Geology,Environmental Chemistry,Microbiology,etc.,with the help of Iinductively Coupled Plasma Mass Spectrometry(ICP-MS),X-ray Fluorescence Spectroscopy(XRF),High Performance Liquid Chromatography-Hydride Generation-atomic Fluorescence(LC-AFS),Scanning Electron Microscopy(SEM-EDS),X-ray Diffraction(XRD),X-ray Photoelectron Spectroscopy(XPS),Fourier Infrared Spectroscopy(FTIR)and other analyisis methods were used to charcterize the tailing mineralogy and to investigate the separate possibility between primary and secondary minerals of arsenic tailings in Hunan Shimen realgar mine.Accordingly,anoxic/anaerobic micorcosm experiments were used to investigate the interaction between microbes and arsenic minerals,then to compare the difference between differet microbes types(ex.,sulphate-reducing bacteria SRB,iron-reducing bacteria DIRB and iron-oxidizing bacteria A.ferroxidans).Besides,the impact of other non-biological factors(ex.,carbon source,sulfate,calcium,and Fe(III))on the As release was also discussed to help understand the As biogeochemical cycle in arsenic-bearing tailings,which might provide experimental evidence for arsenic tailing wates remediation.The main findings in this paper are as follows:(1)Two types of arsenic tailings in Shimen realgar mine(oxidized arsenic iron-bearing tailing and iron-deficient realgar tailing)were found through the field geological survey in the Shimen realgar mine(Hunan).Taking oxidized arsenic iron minerals as the research object,the SEM-EDS,XPS,XRD and FTIR found that it was mainly composed of primary mineral gypsum and secondary minral arsenic iron(hydro)oxides.In-situ ATR-FTIR spectroscopy and centrifugation were combined used to explore the feasibility of separating the primary and secondary minerals in arsenic tailings.The study showed that the relative centrifugal force RCF(Y)and sulfate absorption peak intensity(X)at1113 cm^-1 in FTIR spectra follow the quantitative relationship of Y=-2380*ln(x)+39.72(R²>0.99),and 8000 rpm is the optimal separation speed.Therefore,centrifugation combined with ATR-FTIR characterization might become a method to separate tailings wastes,which can provide a theoretical basis for the recycle of useful components in Shimen realgar arsenic tailings.(2)Under anaerobic condition,sulfate-reducing bacteria(SRB)can significantly promote the reductive dissolution of arsenic tailings,and the soluble As(III)and As(T)showed different trends.Soluble As(III)is the main species in the sediment/water dynamic interface,and its concentration is 1200?g/L,which is about 80-100%of As(T).The As trend can divide into two stages:in the first 72 h,As is rapidly released,and then decreased within the following 72-144 h.The arsenic tailing was dissolved under the effect of SRB,firstly As(V)was released and then quickly reduced by biogenic S(-II).Subsequently,soluble As(III)was adsorbed by secondary iron sulfide(Fe S,Fe S₂)or co-precipitated with S(-II)to generate arsenic sulfide,resulting in the dissolved As(III)was fixed again.Abiotic factors like sulfate and calcium played different roles in the As release.The addition of sulfate can enhance the tailing reductive dissolution by SRB,the dissolved As(III)is 1500?g/L,with an increase of 25%.While the addition of calcium can reduce As(III)concentration to 1000?g/L,with a decrease of 16.7%,which due to the production of secondary minerals like calcium arsenate.Besides,the addition of 100m M sodium lactate can increase the release of arsenic,up to 3000?g/L.(3)Under anaerobic condition,iron-reducing bacteria(DIRB)can simultaneously reduce Fe(III)and As(V),significantly promoting the arsenic tailings dissolution.In the meantime,biogenic Fe(II)can promote secondary minral phase change,further to influence As retention and release.The As concentration presents an M-shape trend.At the initial stage,the tailings were reductive dissolved,a small amount of As was released.Meanwhile,the dissolved Fe(II)promoted the solid iron minerals phase transformation,with secondary siderite and magnetite gradually formed,which indirectly causes the secondary activation of As,leading to more As release,and then dissolved As was fixed again.Besides,the major As speciation and maximum concentration were significantly different in different level of Fe(III)(0.1,1 m M)and sodium lactate(1,10,100 m M).The addition of 1 m M Fe(III)significantly increased the As release,which can reach to 50,500?g/L,and As(V)was the major species(54-100%);while in the 0.1 m M Fe(III)treatment,the maximum As release was only 4350?g/L,and As(III)is the major species(71-100%).Besides,more sodium lactate was added,more As(T)were released,and the pecentage of As(III)was also increased.(4)In the effect of different level of exogenous zero-valent iron(ZVI)(0,0.2,2 g),the dissolution of realgar by A.ferrooxidans presents differnt As species and release in the three experiment stages.During the dissolution,As(II)in realgar firstly is oxidized to As(III),and then further oxidized to As(V).High amount of ZVI addition(2.0 g)can significantly inhibit As release(0.2 mg/L)compared to no ZVI addition treatment(30mg/L.Higher amounts of crystalline As-bearing Fe oxyhydroxides(F3)are produced in high ZVI(2.0 g)experiments(33,62 and 58 mg/kg per stage)compared with the 0 g ZVI addition experiments(17,21 and 18mg/kg per stage).