Phosphate removal from solution using powdered freshwater mussel shells

Freshwater cultured pearl sites discharge plenty of freshwater mussel shells, and most of them are dumped into the landfills. Freshwater mussel shells were studied as recycling resources for phosphate removal from solutions. Laboratory-scale batch experiments were conducted to evaluate the effectiveness of mussel shells in removing phosphate from aqueous solutions. Major factors such as initial phosphate concentrations, contact time, adsorbent concentrations, shells modification and solutions pH were investigated. The main results are summarized as under: 1. Time, pH, concentration of adsorbents and adsorbate are all the function of phosphate removal. 2. By calcination of mussel shell powder at 700 degrees C for 20 min, the phosphate removal capacity is enhanced, from 25% to 55%, when the pH is 5.5. 3. By oscillation in citric acid (2%) for an hour, more than 90% of the phosphate adsorbed on the adsorbent dissolves out. 4. With adsorption isotherm tests, the Temkin and D-R equations are suitable with all three types of the shells, so their adsorption is a chemical adsorption. The saturation adsorption capacity (mg P/g) of natural mussel shells is 6.95. These experimental results suggested the application of mussel shell powder as an excellent adsorption material for removing phosphate from aqueous solutions. (C) 2011 Elsevier B.V. All rights reserved.