Study On Preparation Of Hydroxy Iron Sulfate Sludge-based Biochar And Adsorption Of As³⁺

The disposal of municipal sludge and the remediation of As polluted water are two major problems in China.In this paper,the modification of common municipal sludge into hydroxy iron sulfate sludge（Referred to as: hydroxyl sludge）by Acidithiobacillus ferrooxidan（Referred to as: At.f）was studied,and the conditions of hydroxyl sludge pyrolyzed to hydroxy iron sulfate sludge-based biochar（Referred to as: hydroxyl biochar）were investigated.The relationship between the carbonization temperature and the structure of the hydroxyl biochar was discussed,and the adsorption properties and influencing factors of the biochar on the As³⁺ were also studied.The following conclusions are listed in parallel:In order to meet the metabolic demand of At.f,the bio-leaching process should be supplemented with 0.5g/L of Fe²⁺.The critical carbonization temperature of the hydroxyl sludge was 200℃ and rapid weight loss temperature was concentrated at 200-500℃.The hydroxyl sludge weight has been reduced to 56% when the carbonization temperature added to 500℃.Then,the hydroxy sludge is further carbonized to hydroxyl biochar,Finally,six kinds of hydroxy biochar with carbonization temperature of 300,400,500,600,700 and 800℃ were obtained,and the yield was reduced from 77% to 53%.The structural properties of hydroxy biochar prepared by carbonization at 300-800℃ were characterized by thermogravimetric analyzer,elemental analyzer,specific surface area analyzer,scanning electron microscopy（SEM）,fourier transform infrared spectrometer（FTIR）,and the results are as follows: The thermal stability of biochar is higher than the sludge,and the higher the carbonization temperature is,the more stable the biochar is.With the carbonization temperature increasing,the pH and pHPZC of hydroxy biochar were gradually increased,the content of N and H were decreased,the C element decreased first and then became constant,the BET surface area increased gradually and greater than that of hydroxyl sludge,the type and quantity of the surface functional groups decreased or disappeared gradually,surface pores are more and more developed,square crystal began to appeared at 600℃ and over the surface at 800℃.In the adsorption experiment,the carbonization temperature only affects the adsorption rate of the hydroxy biochar in the early stage of adsorption,and does not affect its final adsorption capacity.The adsorption capacity of 600℃hydroxy biochar was lower than the other hydroxy biochar may related to its high pHpzc.The pH,carbonization degree,thermal stability and surface properties of hydroxyl biochar at different carbonization temperatures were comprehensively analyzed.Finally,650 ℃ hydroxyl biochar was chosen as the object of further study.Study on adsorption performance of As³⁺ in waters by the hydroxyl biochar.The adsorption kinetics and isotherm of the hydroxyl biochar were in accord with the pseudo-second order kinetics and Langmuir isotherm,respectively.The similarity coefficients of adsorption kinetics and isotherm were 0.9994 and 0.9974,respectively.The equilibrium adsorption capacity was 0.48mg/g and the maximum adsorption capacity was 4.7664mg/g.Under the condition of 5mg/L As³⁺ dosage and 10g/L adsorbent dosage,the removal rate of As³⁺ from hydroxyl biochar was 95%.The adsorption amount of hydroxyl biochar for As³⁺ was 0.483mg/g,which is 1.16 times than common biochar.The desorption amount of hydroxy biochar was 0.005mg/g,which is only 27.34% of ordinary biochar.The effects of simulated environmental factors on the adsorption of As³⁺ by hydroxyl biochar were test,The results showed that ambient temperature,solution pH,coexistence anion（SO42-、PO43-）all affect the adsorption of hydroxyl biochar.The adsorption of hydroxy biochar on As³⁺ at temperatures of 33,27 and 15℃were 0.48,0.47 and 0.24mg/g,respectively.The results showed that the environmental temperature did not affect the adsorption of hydroxyl biochar at room temperature and above,but the low temperature will affect.The adsorption capacity of ydroxyl biochar on As³⁺ from different pH solutions is : pH=7（neutral）> pH=5（weak acidity）> pH=9（weakly alkaline）> pH=2（strong acidity）> pH=12（strong alkaline）.The best adsorption of hydroxyl biochar is in neutral solution,the acidic or alkaline solution will affects the adsorption.SO42-had no effect on the adsorption of hydroxyl biochar,and the adsorption capacity was kept at 0.48mg/g.PO43-has an effect on the adsorption of hydroxyl biochar,when the PO43-concentration in solution from 0 to 0.1mol/L,the hydroxyl biochar adsorption amount decreased from 0.46 to 0.11mg/g.