Experimental soil acidification

A laboratory experiment was designed to investigate the interaction of acid mine drainage (AMD) with soils. The study used 3 undisturbed cambisol columns from the mining region of Banská imagetiavnica, imageobov (Slovakia). Columns were acidified with AMD emerging from the mine wastes rich in pyrite, with pure H2SO4 solutions of equivalent concentration (0.15 M H2SO4) or with distilled water. The experiment was performed for 30 weeks. The pH of H2SO4 leachates decreased from 4.1 to 3.3 and was accompanied by increasing amounts of dissolved Al. Progressive acidification increased leaching of major cations Ca, Mg, and K. Acidification of the soil with AMD produced leachates with a pH close to 3 and a high content of different cations and sulphates. Almost 100% of the Fe and 25% of the Al added with AMD were retained in the soil column. Leaching of alkali-earth and alkali cations from the soil by AMD was much lower than by H2SO4 solution. Analyses of solid samples from the 3 columns used selective extractions, XRD and analytical electron microscopy. These showed the different formations and transformations of minerals in acidified columns: amorphous Fe-oxyhydroxides were formed in both AMD and H2SO4 leached soils in the form of a characteristic “mohair” structure rich in Al and Si when AMD was applied. Clay minerals were hardly affected in these samples, in contrast with samples from the H2SO4 acidified column where dissolution of vermiculite, transformation of chlorite, and precipitation of Si gel were observed. Thick Fe-coatings on particles and within the pores of soils leached with AMD change their micro-aggregation and so inhibit the dissolution of phyllosilicates.