Optimization And Mechanism Investigation Of Ni(?) Removal From Aqueous Solutions Using Microbial Flocculant GA1

With the rapid development of social economy,the problem of heavy metal pol-lution is increasingly prominent.Nickel is one of the common heavy metal,it is widely used in various industries,so the water pollution problem of nickel has become in-creasingly serious.The nickel ion in the water will have a big impact on environment and humans.At impermissible levels of exposure,Ni(?)has potential to produce a va-riety of pathological effects on humans,and it can even cause the cancer.Therefore,effective prophylaxis and treatment of Ni(?)from industrial effluents has a primary importance to human life and health.In this study,the incomplete neutralization precipitation was used to build a suit-able system of flocculation and biosorption,and the collaboration of flocculation and biosorption of microbial flocculant GAl(MBFGA1)were fully utilized.The response surface methodology(RSM)was employed to optimize the relevant conditions in the process of biosorption and the response surface optimization.In order to investigate the mechanism,biosorption behaviors,fourier transform-infrared spectra and envi-ronmental scanning electron microscope were studied.The contrast experiment of five kinds of heavy metal solution explained that the promotion of MBFGAl in Ni solution has not been fully reflected.Under the precon-dition of platform period of Zeta potential,in order to embody promotion of MBFGAl,the kaolin,bentonite,calcium oxide were acted as the carrier and added in solution.The results of experiment showed that the removal rate of Ni(?)change had an obvi-ous increase when adding CaO in solution,under the condition of this experiment the value of increase was 11.10%.Based on neutralization and sedimentation of heavy metals,after the addition of quantitative alkaline reagents(NaOH and CaO)the variation of Zeta potential and pH of Ni(?)simulative wastewater contained the same rising period,platform period and declining period.In order to lower pH and make the MBFGAl fully embody its floc-culation and biosorption performance,the platform period were selected for next ex-periments.In other words,incomplete neutralization precipitation during the platform period was the precondition of subsequent experiments.Three points(left,middle,right)of Zeta potential platform were chose for studying the effect of MBFGA1 dose on the flocculation and biosorption.The removal rate of Ni(?)could increase by ap-proximately 12%at most and the maximum biosorption capacity of MBFGAl could reached about 178.25 mg g-1 when the alkaline reagent was CaO,however the varia-tion was not obvious after adding NaOH.Moreover,the removal rate and biosorption capacity had the same regularity of changes when adding CaO,they increased to maximum value when the stirring time was 90 min and then they were comparatively stable.But he variation was not obvious after adding NaOH.Consequently,these ex-perimental data proved CaO was a more appropriate alkaline reagent than NaOH in this research.According to response surface methodology,the optimal and predictive conditions were CaO 0.065g,MBFGA1 11.99mL,stirring time 61.97 min,and under these condi-tions,the removal rate and the biosorption capacity of MBFGA1 could reach 99.35%and 225.16 mg g-1,respectively.According to the study of biosorption behaviors analysis,the Langmuir isotherm model presented a better correlation compared to the Freundlich isotherm,and we could preliminary deduce that the biosorption behavior between MBFGA1 and Ni(?)was a monolayer adsorption characteristic;the correlation coefficient of the pseu-do-second-order kinetic model was higher than that of the pseudo-first-order kinetic model,and the experimental data suggested that the biosorption of Ni(?)onto MBFGAl were mainly chemisorption or ion exchange;the negative values of AG°(Gibbs free energy change)indicated biosorption process was spontaneous,the positive values of AH°(enthalpy change)demonstrated that the biosorption process was endothermic,the positive values of ?S°(entropy change)showed the increasing ran-domness at the solid/solution interface during the biosorption.According to the fourier transform-infrared spectra(FT-IR),environmental scan-ning electron microscope(ESEM)and energy dispersive spectrometer(EDS)analyses,it indicated that adsorption bridging and precipitation enmeshment were the main mech-anism,besides,flocculation and biosorption of MBFGAl supplemented each other and had a closely relationship so that the collaboration would have a significant effect on removal of Ni(?).