Formation Of Biogenic Iron Minerals In As (Ⅴ) And P(Ⅴ) Coexisting Solutions And Their Response To Environmental Conditions

Acidithiobacillus ferrooxidans(A.ferrooxidans)and its soluble extracellular polymeric substances(EPS)can effectively regulate the formation of iron minerals such as schwertmannite and jarosite.These sulfate iron minerals can remove heavy metals and eutrophic elements in polluted water by mechanisms such as adsorption,co-precipitation and ligand exchange.And the formation of iron minerals and its removal of toxic elements are affected by environmental conditions such as pollutants and pH value,temperature and anion of Cl-/SO42-,and cationic Na+/NH4+/Fe3+/Fe2+.In this dissertation,considering the above the mentioned impact factors,we research formation of iron minerals in A.ferrooxidans cultures and EPS solutions,using the various characterization methods,and also examine removal of the coexisting As(V)and P(V).The obtained main results are as follows:In the iron bacterial culture system,the iron minerals mainly containing jarosite formed in the reaction solutions with the lower concentrations of As and P(As/P=1.0/0.1,1.0/0.5,2.5/0.1)after 5 days.While iron phosphate as mainly phase formed in the solutions with the higher concentration of As(4.0 g/L)and P(1.0 g/L)within the whole reaction period.The effect of the low-concentration P on the concentration change trend of low-concentration As shows a sharp declined and then rose to a stable value;while in the other treatments,the effect of P on the concentration change trend of As shows a constant decrease to a stable value.The effect of As on the concentration change trend of low-concentration P is that it droped sharply to a stable value within 24 h,but when P=0.5 g/L,P concentration slowly fluctuates within 12～60 h and then returned to a stable value.In the P=1.0 g/L treatment group,the effect of As on the concentration change trend of P is shown as a steady decline.In the EPS solution system,jarosite formed in the EPS reaction solutions containing the low concentration of As(0.3 g/L)and P(0.1 g/L),while in those solutions with the higher concentration of As(0.7 g/L)and P(0.5 g/L)there are mainly iron phosphate.In the EPS solutions,removal of As is reduced.The addition of As is beneficial to removal of P in solutions of the low-concentration P(0.1 g/L)treatment,but not to removal of P in solutions of the high-concentration P(0.5 g/L)treatment.In the EPS solutions initially with As at 0.3 g/L and P at 0.1 g/L,the addition of Cl-/SO42-sodium salt has no effect on the mineral phase of iron minerals.The iron precipitation products are mainly jarosite,which has little significant difference in the removal of As and P.While adding Cl-/SO42-ammonium salt,the iron precipitation products contain ammoniojarosite,so it is beneficial to the removal of As and P.When the added Cl-concentration is too high,it will inhibit the hydrolysis of Fe3+ to form minerals,which is not conducive to the removal of As and P in the solutions.The addition of Fe3+ salts is not conducive to the formation of iron minerals,so the removal rate of As and P in the solution will be reduced.While the addition of Fe2+ salts has a certain promotion effect on the formation of iron precipitates,so the removal rate of As will increase,but there is little effect on the removal rate of P.In EPS solutions containing 0.3 g/L As and 0.1 g/L P,when the initial pH value is less than 2.2,iron minerals hardly formed,so it has little effect on the removal rate of As and P.When the initial pH value is adjusted by NaOH from 2.2 to 2.5 or 2.8,the formation of iron precipitates increase,and the removal rates of As and P also increase.When the reaction temperature is less than 25℃,it is not conducive to the formation of iron minerals in EPS solutions.When the reaction temperature ranges in 35～45℃,a small amount of iron precipitate forms in the EPS solutions,but the effect on the removal of As and P in the solutions is unobvious.The above results provide a theoretical basis for the removal of coexisting pollution elements in acid mine drainage.And the results also provide practical significance for the biological mineral removing pollutants in complex environments.