Journal of the Korean Society of Mineral and Energy Resources Engineers ISSN:2288-0291(Print) 2288-2790(Online) 한국자원공학회지

Although there are several alternative means of acid mine drainage(AMD) treatment, alkaline neutralization and precipitation, in particular, using the lime due to its relatively low cost and abundance, is preferred method for treating AMD. The current state-of-the-art lime neutralization process for treating AMD is called the High Density Sludge(HDS) process. HDS is a process that has been developed to achieve greatly increased sludge densities compared to those resulting from conventional pH modification systems. This study was carried out to evaluate the variation of sludge properties and removal of metals during recycling of the sludge. The raw AMD was the acid leachate occurring at the waste rock dump of the Samtan coal mine, located in Kangwon province. The neutralization and settlement of sludge took place in batch scale test. Sludge was recycled, as a volumetric ratios of 20%, 40% and 60% and pH was controlled near 9.5 when the raw AMD and sludge were added in neutralization beaker. The chemical analysis for treated water revealed that removal efficiencies of Fe, Mn and Al were over 90% and first two elements, except Al, could be lowered below the regulated limit of 2mg/l. However, removal of SO4 was marginal and removal efficiency of SO4 was about below 60%. The increment of sludge density was correlated with the volumetric ratios of recycled sludge. After 17th sludge return neutralization, thickening of sludge reached 2.5 times to 15.9 times compared to the sludge from the initial neutralization according to return sludge ratios.