Study On Fe(Ⅲ)-induced Siderite Synergistic Treatment Of Cr(Ⅵ) Wastewater With S.oneidensis MR-1

Cr（VI）pollutants contained in water bodies can seriously affect human health and ecosystem stability.Removal of Cr（VI）by coupled biological reduction-chemical reduction is an efficient and stable treatment method.As a widely existing iron-bearing mineral material,siderite attracts widespread attention in environmental remediation.Shewanella oneidensis MR-1,as a facultative anaerobic iron oxide reducing bacteria,has a strong reducing effect.In this paper,mechanochemical ball milling was used to co-grind siderite and Fe₂（SO₄）₃?5H₂O to investigate its removal effect on Cr（VI）.Activate siderite were used in combination with Shewanella oneidensis MR-1,and activated siderite-Shewanella oneidensis MR-1 synergistic Cr（VI）removal system was proposed to investigate its remove effect on Cr（VI）.Humic acid was introduced to explore the effect of humic acid on the removal of Cr（VI）by the activated siderite-Shewanella oneidensis MR-1synergistic system.The main research contents are as follows:（1）The active Fe（II）of siderite was stimulated for removal of Cr（VI）by the activation of siderite by mechanochemical method under the condition of co-grinding of Fe₂（SO₄）₃?5H₂O.Various conditions in the ball milling process were studied to determine the best removal conditions of Cr（VI）;the effects of other salts during co-grinding and the effects of environmental factors on the removal of Cr（VI）from the activated siderite were explored.When the dosage was 4 g/L,the removal effect of 99.6%was achieved after 3 h of reaction.XRD analysis showed that co-grinding made siderite tend to amorphize and activated the properties of the siderite surface.SEM-EDS patterns showed that the co-grinding of siderite and Fe₂（SO₄）₃?5H₂O changed the structure of siderite and produced more active Fe（II）,and the patterns after the reaction with Cr（VI）showed that there were chromium element and chromium valence changes in the product.FT-IR spectrum showed the existence of Cr-O,indicating chromium is involved in the reaction.XPS valence analysis expressed the change of valence state and element content before and after the reaction of Fe and Cr（VI）,which indicated that Fe（II）was reducing play a key role in the reaction.The main removal mechanism was the reduction reaction of Fe（II）in the liquid phase and the solid-phase active Fe（II）with Cr（VI）,the reduction products were deposited in the residue in the form of Cr（OH）₃,Cr_xFe_1-x（OH）₃precipitates.（2）In order to reduce the amount of activated siderite and introduce the form of biological reduction,a activated siderite-Shewanella oneidensis MR-1 synergistic system was proposed to apply for the removal of Cr（VI）.The comparison between the direct mixing system and the co-cultivation system in the microorganism-mineral method,the synergy between activated siderite and Shewanella oneidensis MR-1,and the influence of various environmental factors in the activated siderite-Shewanella oneidensis MR-1 synergistic removal Cr（VI）system were studied.Activated siderite can not only promote the reduction of Cr（VI）by Shewanella oneidensis MR-1,but also can immobilize microorganisms.In addition,the active Fe（II）in activated siderite can also play a role in accelerating electron transfer.Shewanella oneidensis MR-1 promoted the reduction production of active Fe（II）in siderite,ensured the concentration supply of iron ions,and realized the mutual conversion of Fe（II）and Fe（III）.In the activated siderite-Shewanella oneidensis MR-1 synergistic system,the biological reduction and chemical reduction were coupled with each other,which can achieve efficient removal of Cr（VI）.（3）The effect of humic acid widely present in natural environment on the removal of Cr（VI）by synergistic system was explored.Appropriate amount of humic acid can accelerate electron transfer and participate in the reaction of Cr（VI）,but excess humic acid had a slight inhibitory effect on the removal of Cr（VI）by the synergistic system.