Removal of Heavy Metals Using Chemicals Precipitation

Abstract

The single component and multi-component hydroxide precipitation and adsorption were studied for different heavy metals namely Iron (III), Chromium (III), Copper (II), Lead (II), Nickel (II), and Cadmium (II) from aqueous solutions. By using the jar tester Magnesia (MgO) was used as a precipitator at different doses and compared with other chemicals like lime (CaO) and caustic soda (NaOH). The treatment involves the addition of either magnesia or lime-water suspensions (combined with cationic polyelectrolyte, CPE) in various doses, 1.0 – 5.0 g/l for the metal samples to study the effect of varying doses on the treatment efficiency. The results show that the percent removal of metal ions increases to about 99 % with increasing the MgO dose to some limits. The optimum values of MgO doses were found to be 1.5-3.0 g/l. The pH value ranges are 9.5 to 10 with MgO precipitant and pH of 11.5 to 12 with CaO precipitant. In the jar experiment the rotation speed, N, 180-200 rpm, (G of 460-480 s-1) of mixing for two minutes was the most favorable speed of rapid mixing and the slow mixing speed of 15-30 rpm, G of (14-35 s-1), for twenty minutes gave the best results.At the best operating conditions of the pilot plant, the removal efficiency of metal ions was more than 97% at doses of MgO (1.0-4.0 g/l).

Keywords

• removal
• heavy metals
• hydroxide precipitation
• magnesium oxide
• lime
• adsorption