Characterization Of Protonation/Deprotonation And Heavy Metals Binding Properties Of Three Acidophilic Microorganisms

Abstract:Metal adsorption by microbes is an important factor in controlling the transportation, release and reduction pollution of metals in natural systems. However, most investigations have been conducted on neutral mesophile, few investigations have focused on thermophiles. In this paper, we studied (de)protonation and heavy metals binding properties of three acidophilic microorganisms, which are Acidithiobacillus ferrooxidans (A9)(mesophilie) Sulfobacillus thermosulfidooxidans (St)(Moderate thermophile), and Acidianus manzaensis (YN25)(Extreme thermophile). We characterize proton adsorption of the three acidophilic microorganisms by performing acid-base titrations and equilibrium thermodynamics (Donnan model) to calculate the site and site concentration of proton adsorption by the microbes, and the role of EPS of microbes in proton adsorption. We also conducted the effect of initial metal ions concentration, reaction time, pH value, metal types (Cd2+、Cu2+、Zn2+、Ni2+), different biomass, and co-metals on the metals of adsorption, and got the maximum capacity of metal adsorption and affinity of the three acidophilic microorganisms by Langmuir isotherm and Freudlich isotherm, while the Protofit was applied to obtain the pKa values and site concentrations of metals adsorption by the three acidophilic microorganisms. Attenuated Total Reflection Fourier Transformed Infrared Spectroscopy (ATR-FTIR) was applied to analyze the functional groups for metal adsorption.At tha same time, we study the role of extracellular polymeric substances in metals adsorption by three acidophilic microorganisms. We observed that the capacity of proton adsorption of acidophilic is related to the microbial species and EPS, and the buffering capacity increased with site concentration. The binding capacity of metals was related to the kind of microbial speices, initial meatals concentration, reaction time, pH, biomass and co-ions. With increasing metal concentrations, there was a steady enhancement in metal adsorption for all the four test cations within a concentration range, and bacterial metal uptake reached their maximum adsorption quantities from pH8.0to9.0. Generally speaking, major co-ions had a significant negative impact on the uptake of all four target metals, few co-ions had a significant positive impact on the uptake of all four target metals. The result of Langmuir、Freudlich isotherm and Protofit indicated that metals adsorption of microbel is related to the maximum metals adsorption capacity, affinity, pKa value and site concentration.(ATR-FTIR) indicated that hydroxyl, carboxyl and phosphoryl groups play a major role in metals adsorption.