EXAMINATION OF CRUSHED LATERITE BRICK FOR REMOVAL OF CHROMIUM AND ARSENIC FROM WASTEWATER

Adsorption is one of the highly efficient methods to treat heavy metals in wastewater. Due to their economic feasibility, the use of locally available low-cost adsorbents has received much attention, especially in developing countries. The objective of this study was to investigate the applicability of laterite grains made from crushing laterite brick in Vietnam (0.105–2 mm) for the removal of chromium (Cr) and arsenic (As) from wastewater. For comparison, commercially available zeolite and Autoclaved Aerated Concrete (AAC) grains were tested. A series of laboratory tests for examining the effects of the initial metal concentration, initial solution pH, background ion concentration (ionic strength), and solid-to-liquid (S:L) ratio on adsorption and desorption characteristics were carried out. The test results showed that the Langmuir model captured well all obtained data in concentration range of 0–2,000 mg/L for laterite grains, suggesting that monolayer adsorption dominantly occurred. The measured maximum adsorption capacities of laterite grains were 8.2 mg/g and 1.3 mg/g for As and Cr, and the laterite grains gave a relatively high As adsorption compared to previously reported materials. The removal efficiencies of Cr and As were dependent on initial pH and S:L ratio, and lower initial pH and S:L ratio gave higher removal % for all tested adsorbents. Based on the results for desorption tests, laterite grains gave a higher hysteresis index for As (480%) compared to those from zeolite (128%) and AAC (176%), indicating that the tested laterite in this study possessed a strong irreversibility for adsorbed As (i.e. As immobilization). Consequently, laterite grains have a high potential as a low-cost adsorbent for As removal from wastewater.