Pedogenic carbonates for the treatment of acid mine drainage (AMD). Laboratory experiments

Abstract

One of the main problems in mining areas is the generation of acid mine drainage (AMD), which has a negative impact on the environment and human health due to the high concentrations of potentially toxic elements. Several treatments exist that use different types of rocks and processes for the control of acid drainage; among them, limestone is an excellent neutralizer. Another neutralizer is carbonate with pedogenic origin; however, there are no studies evaluating its usefulness. The present work aims to evaluate experimentally the capacity of a carbonate pedosediment and a limestone to neutralize and retain the potentially toxic elements (PTE) of acid drainage from an abandoned mine. The study involved a chemical, mineralogical, geochemical, and micromorphological characterization of the two materials formed from calcium carbonates with different origin (pedosediment and limestone), with the aim of conducting batch treatment tests using pedosediment and AMD with ratios of 1:2.5 and 1:20 (solidg: liquidmL), limestone and AMD with the same ratios. The pH and electrical conductivity of the drainage were measured at the first hour and then every 24 hours until stabilization, which occurred at 259 hours with each neutralizer. The final pH values in both experiments changed from acid to neutral. On the other hand, the electrical conductivity was lower in treatments with limestone than in the pedosediment, especially in the ratio of 1:2.5, possibly associated with a higher salt content. Additionally, the chemical results in the AMD after the tests indicates a high retention of Cu, Fe, Ni, Al and Cd in the limestone and pedosediment relation 1:2.5. Zn retention was achieved up to concentrations below the maximum permissible limits. In contrast, in all treatments Mn is released from the solid phase, with a higher concentration in the limestone. The pedosediment is considered efficient in the neutralization and precipitation of the PTE. Results were better with the ratio 1:20, because 1:2.5 had higher concentrations of Na+ and Cl-that can be a problem of salinity.