Utilization of foundry sand waste as heavy metal sorbent

Waste foundry sand is one of by-products from metal casting operations. Nowadays, there are 494 foundry industries in Thailand which discard 3.4 million tons of spent sand in landfill per year. Primarily, this sand is a mixture of sand, clay, coal dust and fine residual iron particles. The objective of this study was to assess the feasibility of using waste foundry sands as a low-cost sorbent. The tests were also conducted on iron filing, bentonite and coal dust for comparison. Synthetic foundry sand was synthesized to compare the removal efficiency of zinc onto waste foundry sand and synthetic foundry sand including enhanced the removal efficiency of synthetic foundry sand by using a multivariate regression analysis to optimize the proportion of significant index parameters for the best removal efficiency. Batch experiments and analytical modeling were conducted in this work. Leaching characteristics of the waste foundry sands were evaluated. The result showed that heavy metals in leachates from waste foundry sands were less than the values from the Ministry of Industry’s standard. The zinc removal efficiency using initial zinc concentration 50 mg/1 ranged from 12.95 - 51.02 % at initial solution pH of 3.72 and ranged from 58.74 - 84.77 % and 68.75 - 92.39 % for initial solution pH 6.59 and 8.01, respectively. Empirical equations developed using multivariate regression indicated that sorption capacity of zinc was a function of iron content, clay content and total organic content. Particularly, high pH value enhanced zinc removal by sorption and precipitation. Comparison between spent foundry sand and synthetic sand follow the proportion of spent sand that has the great sorptive capacity showed that the removal efficiency of zinc by synthetic sand was slightly higher than that of waste sand and zinc removed byenhanced synthetic sand was comparable with prediction from regression equation.