Removal of heavy metals from contaminated waters and waste waters has been always one of the important environmental issues. There are different methods for removing heavy metals from contaminated waters. Among these, adsorption with a low-cost adsorbent has been found to be an economical and reliable method, which can easily remove many pollutants from water by employing proper adsorbents. In this research nano-size and nanocrystalline hydroxyapatite powders with average crystal size of 18-60 nm were produced from bovine bone, by thermal treatment and mechanical milling with a high energy planetary ball mill. The produced powders were used as adsorbent to remove lead ions from aqueous solutions. At this stage of the work, the effects of heating time and temperature on the properties of produced powders, were investigated. On the basis of obtained results, heating temperature and time of 750 o C and 4 hr, respectively, were found the optimum conditions for hydroxyapatite production with proper crystallite size from bovine bone. Adsorption experiments were designed using Taguchi method and effect of such operating parameters as initial lead concentration in the solution, initial pH of the solution, adsorbent mass, and ball mill time on the percentage of lead removal were investigated. To reduce the potential costs of separating nano-size adsorbent powder from treated water, the hydroxyapatite powder was shaped with alginate as a natural polymer. For this part of the work, optimum milling time of 2 hr, was also determined by Taguchi method. After choosing optimum powder, alginate- hydroxyapatite composite adsorbents with 20 and 50 wt% of hydroxyapatite, were produced in the forms of beads and film. Adsorption capacity of the composite beads was less than that of alginate and hydroxyapatite adsorbents alone, while film composite adsorption was more than those of two other adsorbents alone. By using film composite adsorbent which contained 50wt% of hydroxyapatite, lead removal increased about 13.56% and 22.29% in comparison with alginate and hydroxyapatite adsorbents, respectively. Effect of ultrasound irradiation on the adsorption capability of the powders which were milled from 2 to 16 hr , was also investigated. It was observed that by using ultrasound irradiation adsorption ability of powders increased significantly, from 53.8% up to 122.1% for the powders with different milling times. Keywords : Nanocrystalline hydroxyapatite, Adsorption, Taguchi, Alginate, Heavy metal
