COPPER REMOVAL FROM CONTAMINATED GROUNDWATER USING NATURAL AND ENGINEERED LIMESTONE SAND IN PERMEABLE REACTIVE BARRIERS

摘要

This work investigates the performance of natural and engineered limestone sand (thermally and chemically modified) with respect to copper removal from groundwater protected by permeable reactive barriers. The engineered sorbents (particle size 0.25 - 0.50 mm) were prepared using high temperature at 850℃ and solutions of 0.25M Fe(Ⅲ), 1M NaOH and 1M HNO_3. Batch tests were carried out using a constant mass of the sorbent (0.5 g) and 50 mL of numerous copper ion solutions at different pH values at a desired shaking time in order to analyze the mechanism of copper removal. At a final pH value above 6.3, natural and engineered limestone sand removed over 94% of Cu(Ⅱ). Test data indicated that the mechanism of copper removal is significantly affected by the contact time and the final pH level. The main processes leading to the removal of copper ions included precipitation with calcite or carbonate solids, chemisorption and physisorption. The test data fitted well with the pseudo-first-order, pseudo-second-order and intra-particle diffusion kinetic models (excluding data for Fe(ffi)-modified limestone) as well as the linear Henry's isotherm. The most suitable for further application as a reactive material in PRBs technology is NaOH-modified limestone, followed by thermally-modified, HNO3-modified, Fe(Ⅲ)-modified limestone, and limestone.