Effects Of PH And Organic Acid Salts On The Stability Of Arsenic/chromium Sulfate Iron Minerals During Aging

As sulfate iron minerals widely existing in acidic mine wastewater environment,schwertmannite and jarosite display good adsorption and co-precipitation effects on As(?)and Cr(?).However,with the change of the external environment,the schwertmannite and jarosite may undergo dissolution and mineral phase transformation due to their metastable properties.In this process,the originally removed As(?)and Cr(?)re-release.In order to understand the mineral phase transformation of As/schwertmannite and Cr/jarosite and the release rules of As(?)and Cr(?),the extracellular polymer-containing solution(EPS)after removing cells from the culture solution of Acidthiobacillus ferrooxidans(A.ferrooxidans)was used to simulate the acidic mine wastewater environment,and to explore the effect of changes in external environmental conditions(pH value and organic acid salts)on the stability of biosynthesis of As/schwertmannite or the synthesis of Cr/jarosite by EPS co-precipitation.The iron minerals were characterized by X-ray diffractometer,infrared spectrometer and scanning electron microscope.And the concentrations of As(V),Cr(VI)and Fe ion in solution were measured by inductively coupled plasma spectrometer and visible spectrophotometer,respectively.The results were as follows:Schwertmannite and 21.8 wt%As/schwertmannite prepared by biological methods.Schwertmannite was composed of sea urchin-like spherical particles with a particle size of 1.30 ?m.As/schwertmannite was composed of smooth ellipsoidal particles with a particle size of 40?100 nm.Jarosite and 1 wt%Cr/jarosite prepared by EPS coprecipitation were composed of smooth diamond-shaped massive particles with a particle size of 1.0?2.0 ?m.In EPS solution(initial pH 2.0),the addition of As(?)could accelerate the transformation of schwertmannite to jarosite and inhibite the crystal growth of minerals.And the addition of Cr(?)could enhance the jarosite crystallinity.Finally,the schwertmannite could be transformed into jarosite,and remained stable.As/schwertmannite were transformed into jarosite after aging in EPS solutions with different initial pH values(1.2?2.3)for 180 d.The As(?)concentration in the solution decreased with the increase of the initial pH value of the solution.At pH 1.2,the stability of As/schwertmannite was the worst,and the released As(?)was the most.The large release of As(?)mainly occurred during the ore phase transformation(within 7 d of aging).Cr/jarosite remained unchanged in the ore phase after aging for 180 d in EPS solutions with different initial pH values(1.2?2.3).The Cr(?)concentration in the solution decreased with the increase of the initial pH value of the solution.At pH 1.2,jarosite dissolved the most and released the most Cr(?).The massive release of Cr(?)mainly occurred within the initial 5 d.As/schwertmannite were transformed into jarosite after aging in EPS solutions(pH 2.0)with different oxalate concentrations(OA=0?100 mmol/L)for 180 d.The low concentration of OA(1?50 mmol/L)displayed little effect on the release of As(?)from As/schwertmannite,but the concentration of As(?)in the solution decreased significantly when the concentration of OA was high(100 mmol/L).The large release of As(?)mainly occurred during the ore phase transformation(within 7 d of aging).Cr/jarosite remained unchanged after aging for 180 d in EPS solutions(pH 2.0)containing different concentrations of fulvic acid(FA=0?10 g/L).The addition of FA significantly reduced the release of Cr(?)from jarosite,but the release of Cr(?)increased with the increase of FA concentration.The massive release of Cr(?)mainly occurred within the initial 5 d.The above research results revealed the dissolution,mineral phase transformation and pollutants release of As-schwertmannite and Cr-jarosite.This provided a theoretical guidance for maintaining the stability of As-schwertmannite and Cr-jarosite in actual acidic mine wastewater.