In Situ Immobilization of Heavy Metals in Severely Weathered Tailings Amended with Food Waste-Based Compost and Zeolite

Abstract

Biowastes and inorganic additives are acknowledged efficient but site-dependent alternatives for in situ metal immobilization. The present study evaluates food waste-based compost, a particularly abundant type of biowaste in South Korea, and zeolite as amendments for increasing pH and reducing metal leaching potential in weathered tailings from an abandoned mine site. Two types of biowaste were used: food waste compost (60 % food waste and 40 % sawdust) and market compost (50 % food waste, 10 % agricultural waste, 10 % manure, and 30 % lime). Materials were thoroughly characterized. Leaching tests were then performed in reactors filled with various mixtures of organic-inorganic amended tailings, over a 4-week period. The in situ metal immobilization efficiency of compost was evaluated based on collected leachate quality. Results indicated that both organic and inorganic materials were successful for increasing pH (from 3.0 to up to 8.1) and metal immobilization, except for Pb and As, with which leaching potential increased in most amended reactors relative to un-amended tailings (up to 43 and 158 %, respectively). Over the duration of the experiment, the cumulative reduction of metal leaching potential ranked as follows: Zn (44-91 %)>Mn (4-76 %)>Cr (20-53 %)>Fe (34-44 %)>Cd (17-43 %)> Al (0.5-24 %). Among mixtures, combined biowaste and zeolite-amended tailings showed the best performance for increasing pH (7.5-8.1) and for metal immobilization. Chemical and biological processes, such as sorption and precipitation processes, were predominant. Overall, the study provides useful data on the efficient use of food waste compost for acid mine drainage prevention in South Korea.