Biosorption Of Cu (Ⅱ) And Cd (Ⅱ) By Silica-gel-immobilized Algal Residues

Algal residues, solid wastes in brown algae industrial production, can destroy ecological balance if they are discharged directly into natural water. However, we can use them as biosorbent to remove heavy metals from wastewater due to the abundant functional group in surface. Compared with traditional way in disposing heavy-metal-polluted wastewater, such adsorption has many advantages in the following aspects:higher efficiency but with lower price, higher specificity but with lower-level pollution. Nevertheless, if algal residues are discharged directly into natural water, the cost-recovering are usually very expensive; to crown it all, if we don't recover such algan residues, the secondary pollution comes out due to decomposition of these algan residues.In this work, silica-gel-immobilized algal residues sphere of uniform size and shape were made. Such biosorbent has the following advantages:fist of all, it's recoverable in industrial production with lower cost, and can be filled into certain equipment like packed columns. Secondly, biosorbent can fully contact with heavy metal since interal-porous silica-gel-immobilized ball has large specific area. The third one lies in the functional group of algal residues'surface, which can combine with heavy metal inducing the adsorption process. Furthermore, the raw material can be gotten easily with low price.We investigate the influence of biosorption characteristics of Cu(Ⅱ) from aqueous solutions by silica-gel-immobilized algal residues. The experimental data show that all biosorption characteristics have significant impact on biosorption process such as pH, initial Cu(Ⅱ) concentration and contact time. The removal of Cu(Ⅱ) could reach about 85% when initial Cu(Ⅱ) concentration is below 2mmol/L, and the maximum adsorption capacities is around 0.7-0.8mmol/g at 25℃. We also fit our equilibrium data with Langmuir, Freundlich and Dubinin-Radushkevich isotherm models, and Kinetic features of Cu(II) biosorption is modeled by Pseudo first-order equation and Pseudo second-order equation.Biosorption characteristics of Cd(Ⅱ) from aqueous solutions by silica-gel-immobilized algal residues are investigated. The experimental data show that optimum pH is between 5 and 6, initial concentration and contact time also have impact to biosorption process. We also fit our equilibrium data with Langmuir, Freundlich and Dubinin-Radushkevich isotherm models, and Kinetic features of Cd(Ⅱ) biosorption is modeled by Pseudo first-order equation and Pseudo second-order equation. The adsorption behavior of Cd(Ⅱ) is similar with that of Cu(Ⅱ).The results indicate that silica-gel-immobilized algal residues which have better mechanical strength are selectivable with high pertinency and also can be easily recycled. Thus, the algal residues are suitable for removal of heavy metals from wastewater.