Biosorption Of Cr(Ⅵ) From Aqueous Solutions By Wasteagrocybe Aegerita: Optimization And Mechanism

In recent years, with the rapid development of industry and agriculture and thegrowth of population, the amount of sewage water increased and cause serious waterpollution. This is a severe threat to the water resource, or even endanger the life andhealth of public. The wastewater containing heavy metal ion discharged by variousindustrial activities is nonbiodegradable and highlytoxic, some of these can bebiologically enriched and then lead to health hazard through biologic chain. Amongthe various heavy metal pollution incidents, Cr(Ⅵ)acts as pollution source is moreand more common, and this seriously influences the circumferential animal and plants,even the human health, so it is imperative to deal with the Cr(Ⅵ) in the wastewater.For the present, techniques in treating such wastewater include chemical treatment,physical treatment and biological treatment, and because of its outstandingadvantages: broad-source, excellent absorbability, easily reuse of heavy metal,biosorption is widely studied. Thus, discover and develop efficient and cheapbiosorbent is always the target of scientific workers.In the present work, waste Agrocybe aegerita was applied to remove Cr(Ⅵ) fromaqueous solution and the adsorption performance was studied. Single-factor test wasapplied to study the five main influencing factor: pH, initial Cr(Ⅵ) concentration,contact time, speed of stir and adsorbent dosage. And then the Box-Behnken designmethodology, including five factors: pH, initial Cr(Ⅵ) concentration, contact time,speed of stir and adsorbent dosage, was employed to study the removal ofchromium(Ⅵ) from aqueous solution by wasteAgrocybe aegerita, with the removalof Cr(Ⅵ) as the target response. The thermodynamic characteristics, sorption kineticsand mechanism of the adsorption process were also been discussed. It result indicatedthat the impact of each factor is different, and present respective regularity; pH,initial Cr(Ⅵ) concentration and adsorbent dosage were the three key factorsinfluencing the uptake of Cr(Ⅵ), among these factors, the influence of pH isespecially evident; The optimal adsorption conditions were pH1.19, initial Cr(Ⅵ)concentration148.58mg/L,contact time89.02min, speed of stir180.12r/min andadsorbent dosage10.90g/L,and under these conditions, the removal of Cr(Ⅵ) wasabove96%. Langmuir, Freundlich and Dubinin-Radushkevick isotherms were appliedto fit the adsorption equilibrium data and the adsorption process, and found thatLangmuir isotherm adsorption model was the best reflecting the adsorptioncharacteristics. The adsorption capacity of the biosorbent was46.95mg/g.Apparentthermodynamic parameters, such as ΔG, ΔS and ΔH were calculated and the outcomeshowed that the adsorption process was endothermic and spontananeous, while theperplexity of the system increased at the same time. The pseudo-first-order andpseudo-second-order model were applied to the date, and found that the correlation coefficient of pseudo-second-order model is0.972, thus it was determined as apathway to reach the equilibrium. Finally, the removal mechanism was discussed bydeduction from FTIR images result, and found that the physisorption plays a leadingrole in adsorbing Cr (Ⅵ) along with chemisorption, hydroxyl, carboxyl and aromaticnucleus are the main functional groups. In this study, the results show that wasteAgrocybe aegerita is a good absorbent for removing chromium (Ⅵ) from wastewater,which is a strategy of controlling waste by waste.