Enhancement of the Stability of Biosorbents for Metal-Ion Adsorption

Abstract

Biosorbents have demonstrated great potential in the treatment of metal-containing wastewater. However, one of the bottleneck issues of using biosorbents is that amounts of organic carbon release from biosorbents into water. This seriously limits the application of biosorption technology in treating wastewater. In this work, a novel methodology was developed to greatly reduce the organic carbon release and enhance the stability of biosorbents by using barley straw as the model biosorbent material and nickel as the model metal ion. The raw barley straw was first made into cylindrical pellets, which were coated with a sodium alginate (SA) and poly­(vinyl alcohol) (PVA) membrane. The coating conditions including the ratio of SA to PVA, glutaraldehyde (GA) dose, concentration of CaCl₂ solution, and cross-linking time were optimized by L₉(3⁴) orthogonal array design. The pellets coated at the optimal conditions (1:1 mass ratio of SA to PVA, 1.0 mL of GA, 8% CaCl₂, and 20 min of cross-linking time) were then applied for nickel adsorption. The effects of the solution pH and ionic strength on the adsorption equilibrium and desorption of adsorbed nickel ions were investigated. Scanning electron microscopy and synchrotron X-ray fluorescence spectroscopy were used to locate the adsorption sites on the coated pellets. The results demonstrated that organic carbon release of the coated pellets was significantly reduced to 3.8–9.7 mg/g of dry barley straw pellets in the nickel adsorption process, while that of the raw barley straw particles was 44 mg/g. The nickel uptake increased to 25.6 mg/g, higher than that of the raw barley straw particles