Preparation Of Iron Modified Straw Biochar And Its Adsorption For Hexavalent Chromium In Aqueous Solution

Chromium?Cr?is one of the most dangerous heavy metal pollution elements due to its carcinogenicity and gene mutation.Trivalent chromium?Cr?III??and hexavalent chromium?Cr?VI??are the main forms of Cr in industrial wastewater.In contrast,Cr?VI?is more stable,soluble,and toxic?about 100 times more toxic than Cr?III??.At present,Cr?VI?has been designated as a top pollutant by the international environmental protection agency,which cannot be degraded naturally and will accumulate and accumulate in organisms and human bodies for a long time.Therefore,it is necessary and urgent to study the removal of Cr?VI?from wastewater containing Cr in this context.Taking the simulated Cr?VI?wastewater as the research object,this paper firstly screened the suitable preparation conditions of iron modified straw biochar?FeBC?.Secondly,the physicochemical indexes of FeBC and unmodified straw biochar?BC?were determined and compared.Based on the static sequencing batch adsorption experiment,the adsorption mechanism and desorption regeneration ability of Cr?VI?by FeBC were investigated.The dynamic adsorption mechanism of Cr?VI?by FeBC was investigated.The main research results obtained are as follows:The preparation conditions of FeBC were as follows:modification time 48h,solid-liquid ratio 1:10,iron ion concentration 1mol/L;Compared with BC,FeBC showed no significant change in functional groups,but acidic functional groups increased,while alkaline functional groups decreased.The increase of specific surface area and total pore volume and the decrease of average pore diameter have positive effects on the adsorption of Cr?VI?.In the contrast test,the adsorption rate of FeBC on Cr?VI?was significantly higher than that of BC,and the maximum adsorption rate at the equilibrium moment was 1.73 times that of BC.This result indicated that FeBC was more conducive to the adsorption of Cr?VI?.In the static adsorption process of Cr?VI?by FeBC,the pseudo-secondary kinetic model is more suitable to describe the adsorption process.The results show that the adsorption process of Cr?VI?by FeBC is mainly a chemical adsorption process.The langmuir-freundlich thermodynamic model fitted the adsorption thermodynamic data well,which indicated that Cr?VI?adsorption on FeBC was a multilayer adsorption process.Thermodynamic calculation shows that the adsorption of Cr?VI?by FeBC is a spontaneous endothermic process.SO₄^2-,NO₃^-and Cl^-all had an effect on FeBC adsorption Cr?VI?.According to the regeneration performance evaluation of FeBC,FeBC has a good regeneration ability.0.1mol NaOH solution can be used as the regeneration solution of FeBC.At FeBC to Cr?VI?of the fixed bed dynamic adsorption process,the simulated wastewater flow velocity,FeBC bed height,simulated wastewater concentration and pH value factors for FeBC adsorption of Cr?VI?has a great influence,the results show that the lower waste water solution flow rate,higher FeBC bed height,the higher concentration of waste water,low pH conditions conducive to the dynamic adsorption of Cr?VI?.Both Thomas model and BDST model can well fit the dynamic adsorption process of Cr?VI?by FeBC in fixed bed system.The effects of SO₄^2-,NO^3-and Cl^-on the adsorption Cr?VI?of FeBC in the fixed bed system were consistent with the results of static adsorption.Three analytical agents?NaOH,H₂SO₄,EDTA?can be used to analyze FeBC in fixed bed system.The sequence of effects is NaOH>H₂SO₄>EDTA.With 1mol NaOH as the analytical agent,the unit adsorption quantity qe?mg/g?at the equilibrium of the adsorption column could still maintain 30.19%of the initial adsorption quantity after four cycles of analysis.The experimental results provide some guidance for the industrial application of FeBC.