Effect And Mechanism Of Arsenite (?) Removal From Water With Potassium Ferrate Enhanced By Biochar

Arsenic?As?is toxic and carcinogenic chemical element.In China's the sanitary standard for drinking water GB5749-2006 stipulates that the total arsenic concentration does not exceed 10 ?g/L.Anthropogenic activities,such as mining and smelting,increased the extent of high-arsenic wastewater pollution.Potassium ferrate has effect on As removal due to its oxidizability and adsorbability.However,in view of the high cost or hard transportation and storage,it is essential to study a mothod to reduce the amount of potassium ferrate and improve the removal efficiency of arsenic.There are two valence states of As: As???and As???.As???is more toxic and mobile and harder to be removed.Therefore,this study selected As???as the research object.A small amount of biochar is used to enhanced the removal of As???by potassium ferrate.By comparing the removal rate of As???with potassium ferrate and biochar,it is proved that the removal of As???by biochar enhanced potassium ferrate is better,and the removal rate is up to 90% by increasing 33%.Scanning electron microscopy-X-ray spectroscopy?SEM-EDS?analysis,X-ray photoelectron spectroscopy?XPS?analysis and Fourier Transform Infrared Spectrometer?FTIR?analysis were applied to explore the mechanism of the reaction.EDS showed C element concentration decreased from 82.6% to 65.7%,O element concentration increased from 17.4% to 33.4% after the reaction.XPS showed that the concentration of C=C?C-C and C-H decreased from 76.03% to 31.48%,while the concentration of C-O increased from 21.25% to 29.56%,C=O increased from 1.49% to 30.33% and COOH increased from 1.23% to 8.63%.The potassium ferrate could react with the functional groups on the surface of biochar,so the surface area and adsorbability of biochar were improved.Also,ferric nanoparticles??-Fe2O3 ?Fe OOH?were formed after the reaction and they can adsorb the As???.Then the biochar and ferric nanoparticles were coprecipitated with arsenic from the water.The reaction had good effect in a wide range of p H,especially in p H 6.The effects of different removal methods of As???and some typical cations(Ca²⁺?Mg²⁺?NH⁴⁺)and anions(SO₄^2-?PO₄^3-?B₄O₇^2-),as well as some ions which may have an effect on removal(Fe²⁺?Fe³⁺?Al³⁺)and humic acid,on the removal of As???by biochar-enhanced potassium ferrate were also investigated.It was found that the influences of Ca²⁺,SO₄^2-on As???removal were neglected.NH⁴⁺?Fe³⁺ had little repress under medium concentration.Mg²⁺?Fe²⁺ increased removal rate under low concentration,while Al³⁺ had a contrary effect.had no obvious impact,whereas PO₄^3-showed prohibitive effect on As???removal and the prohibition tendency increased with its concentration.One explain is PO₄^3-can combine with potassium ferrate and accelerate the ferrate autodecomposition.With the increase concentration of B₄O₇^-,a little decline of As???removal was observed.Humic acid will occupy the surface adsorption site of iron oxide,compete with potassium ferrate oxidant,cause the aggregation efficiency of ferrate oxidant to decrease,and complex with As,which makes As difficult to be adsorbed and removed.What's more,the effect of biochar enhanced potassium ferrate system was compared with other methods,oxidants,adsorbents,membranes for example on removal of As???.By comparison,we found that ferrate is a green effective oxidant,which can generate insitu Fe???nanoparticles.Also biochar is a wide range of low cost carbon materials.Biochar enhanced ferrate have advantages of easy operation,high removal rate,short time reaction,easy separation.Biochar enhanced potassium ferrate for arsenic removal has a widely used in practical processes.