Recycled Aggregates Effects on Acid Minesoils Response to Rainfall Events: Short-Term Study

This investigation focused on the response of minesoils to which an upper substrate of recycled aggregates was added. The experience consisted in a first characterization of the minesoils (February’23) and two sampling after rainfall events, occurred in consecutive months (March and April’23). Soil sample reaction (pH-Eh and electrical conductivity) was studied with a portable multiparametric, chemical composition was analysed by X-Ray fluorescence and mineralogy was assessed by X-Ray diffraction and electron microscopy SEM.

Results showed that soil surface became less acidic, changing from 3.6 to up 6 units of pH. It was probed that the alkalinizing lost reactivity at depth, since level b and c were progressively more acid, but also that it was being depleted in time. Redox conditions, nevertheless, behaved in distinct way, increasing at the three levels in time, that could affect the distribution of elements. In fact, content of Al, Fe and S slightly decreased in surface with time, but specially Al increased in depth, suggesting any mobilization to leader elements. On the other side, trace elements, specially As, trended to concentrate at the intermediate level, marking the importance of redox conditions in their distribution.

Initial mineralogy hardly varied along time, maintaining the presence of the main minerals (quartz, mica and jarosite from the soil and calcite and dolomite from the amendment). Anyway, bassanite appeared during treatment, at the time than calcite and dolomite were depleted, showing the interaction of those with sulphur liberated from the oxidized pyrite observed by SEM.