Study On Application Of Algae Biosorbent In The Electroplating Wastewater

The pretreated algae biosorbent was used to treat Au²⁺,Ag⁺,Cu²⁺ and Ni²⁺ ions of electroplating wastewater in this paper. Biosorption isotherm equation, biosorption-desorption kinetics and the reuse efficiency of biosorbent were studied, and compared with previous study. In this work, adsorption features of algae were investigated as a function of initial pH, initial concentration of ions and algal dose, and then the optimal biosorption features were obtained. Based on pilot test experiment of factory treatment of heavy metals by marine algae, the optimal biosorption features was optimized. The major conclusions are summarized as follows:1.pH of solution influences greatly on biosorption capacity of Au²⁺,Ag⁺,Cu²⁺ and Ni²⁺ ions in the water. The optimal adsorption effect of metal ions on algae was observed at pH 4.0-6.0. The percent removal of metal ions was decreased, and biosorption capacity of algae was increased with increasing initial concentration of Au²⁺,Ag⁺,Cu²⁺ and Ni²⁺ ions, while the certain algal dose and metal ions concentration 5-80 mg/L. The biosorption capacity of algae decreased quickly as metal ions concentration beyond 80 mg/L. The algal biosorption is more efficient than the traditional physicochemical methods at low ions concentration. The biosorption efficiencies and capacities of ions showed different variation with increasing biomass concentration. Considering the two aspects: good biosorption effect and saving algal dose, we chose the biomass concentration was 2.50 g/L. So the optimal sorption condition is pH of 6.0, algal dose of 2.50 g/L, particle size of 60 mesh and metal ions concentration being less than 80 mg/L.2.The adsorption process is fast, reaching equilibrium state in less than 30 min. The biosorption process followed Langmuir isotherm model, then the calculated result showed: maximum biosorption capacity of immobilized algae was observed 0.96, 0.53, 7.35 and 38.46 mg/g for Au²⁺,Ag⁺,Cu²⁺ and Ni²⁺,respectively, and the affinity of Ni²⁺ ion with algae was stronger than the other ions. Compared with previous studies, the result indicated: competitive adsorption of Cu²⁺,Ni²⁺ and coexisting Zn²⁺, Cd²⁺ ions lead to the decrease of biosorption capacity of Cu²⁺,Ni²⁺. 3. The first stage adsorption process of Au²⁺,Ag⁺,Cu²⁺ and Ni²⁺ on Laminaria japonica is fast, reaching equilibrium state in 10 min. The biosorption capacities increased a little as the time going. The adsorption process of Au²⁺,Ag⁺,Cu²⁺ and Ni²⁺ on L. japonica followed the pseudo-second order model well (R² was 0.977, 0.995, 0.999 and 0.999, respectively), and the kinetics parameter k₂ was 0.1106, 0.3818, 0.4589 and 2.6912 g/(mg·min), respectively, biosorption capacities (q_e) was 2.52, 0.54, 2.46, 8.62 mg/g, respectively. Compared with previous studies, the result indicated: the order for q_e of algae biosorption on Cu²⁺,Ni²⁺ at equilibrium state was experiment solution > electroplating wastewater, but the order for rate constant of the pseudo-second order model was electroplating wastewater > experiment solution.4. Desorption experiments showed 0.1 mol/L HC1 was an efficient desorption, metal ions Au²⁺,Ag⁺,Cu²⁺ and Ni²⁺ can be desorbed quickly, and the desorption process was similar to adsorption process. The desorption process followed the the pseudo-second order model well (R² was 0.999, 0.998, 0.999 and 0.999, respectively), and the kinetics parameter k₂ was 10.6508, 4.9264, 0.6556 and 0.0312 g/(mg·min), respectively, biosorption capacities (q_e) was 0.20, 0.07, 0.84 and 29.41 mg/g, respectively. The adsorption capacity of desorbed algae was very good, which allowed the reuse of the biomass in three biosorption-desorption cycles without any considerable loss of biosorption capacity.5. The experiments of heavy metal wastewater treatment in three companies indicated that algae biosorbent was a good biosorbent. The mean sorption capacity of algae was 120-180 mg/g, and the concentration of heavy metal ions in the treated wastewater was lower than the nation second grade quality standards. The adsorption features of regenerative allowed the recovery of precious metal from the electroplating wastewater and the reuse of biosorbent simultaneously. Experiment of Wenton Group(Hong Kong) Limited of Fujian showed there was a good recovery rate of precious metal as Ni²⁺,Au²⁺higher than 80 % and Cu²⁺ higher than 50 %. The biosorption-desorption provide a new approach to recover precious metal, and there will be a very good development potential and application prospect.