Study On Preparation Of Yak Dung Biochar And Its Removal Of Arsenic And Fluoride From Water

Arsenic and fluoride are two typical high concentrations of elements in geothermal water in Tibet,In the process of geothermal utilization,tail water discharged directly to the surface will cause water pollution,which will affect human health.In the present work,the abundant biomass energy in Tibet yak dung,was made into a series of biochars?BC500,BC600,BC700 and BC800?by pyrolysis under different temperatures,and the better one was modified by FeCl₂ to obtain modified biochar?Fe-BC600?.Then the basic research on the adsorption of arsenic and fluoride in water was carried out.The results showed that BC600 can remove 64.99%As?V??initial concentration is 4.0 mg/L?at pH=7,temperature 80°C and adsorbent dosage10 g/L;can remove 99.36%F?initial concentration is 19.0 mg/L?at adsorbent dosage4 g/L.Fe-BC600 can remove 99.44%As?V?at pH=7,temperature 80°C and adsorbent dosage 3 g/L,the saturated adsorption capacity was 1.326 mg/g;can remove 98.77%F at adsorbent dosage 4 g/L,the saturated adsorption capacity was4.692 mg/g.Compared with BC600,the saturated adsorption capacity of Fe-BC600for arsenic increased by six times,while the saturated adsorption capacity for fluoride remained unchanged.For BC600,quasi-second-order kinetic equation can better describe its adsorption of arsenic,Quasi-First-Order kinetic equation can better describe its adsorption of fluoride;at different temperatures,its adsorption process of arsenic can be better fitted by Langmuir and Freundlich adsorption isotherm equation,and the adsorption process of fluoride can be better fitted by Freundlich adsorption isotherm equation;the reaction of arsenic and fluoride adsorption is endothermic and spontaneous.For modified biochar Fe-BC600,quasi-second-order kinetic is more suitable for describing the adsorption process of arsenic and fluoride;the adsorption process of arsenic and fluoride at different temperatures can be well fitted by Freundlich isotherm equation;the adsorption reaction of arsenic and fluoride is endothermic and spontaneous.The removal rate of fluoride and arsenic was 97.88%and 98.79%when adsorbed4.0 mg/L As?V?and 19.0 mg/L F simultaneously at pH=7,temperature was 80°C,and the dosage of Fe-BC600 was 4 g/L,which were the same as they were adsorbed alone.In the presence of other ions Ca²⁺,Mg²⁺,Cl^-,SO₄^2-and HCO₃^-,the adsorption efficiency of arsenic and fluoride of modified biochar did not decrease,and the removal rate was still above 98%,which indicated that the five ions had no effect on the adsorption of arsenic and fluoride.0.2 g of adsorbed saturated biochar was placed in 10 mL of 0.1 mol/L HCl solution,after desorption for 40 min,the removal rates of arsenic and fluoride by modified biochar were 97.33%and 94.26%,respectively.After desorption-adsorption for 5 times,the removal rates of arsenic and fluorine were still about 95%and 70%,respectively,indicating that the modified biochar had good regeneration performance.In order to better understand the adsorption process,biochar and modified biochar were characterized by BET,FTIR,XRD,SEM and XRF,respectively.This study provides a new way for Tibet to use local resources to solve local environmental problems.