Leaching Experiments to Delineate Factors Governing Rock–water Interactions: Case of the North- Western Part of the Volta River Basin of Ghana

Abstract

Leaching experiments were carried out on five silicate rock samples from the various geological units of the North-Western part of the Volta River Basin of Ghana. Four experimental conditions were tested: (1) room temperature experiments opened to only atmospheric conditions, (2) at a temperature of 50ºC, (3) experiment saturated with CO2 gas and (4) in acid environment (HNO3 & H2SO4). The aim of this study was to investigate the effects of these conditions on rock-water interactions that influence groundwater chemistry in the study area. Mineralogical composition of rocks analyzed prior to the experiment, through petrographic microscope and X-ray Diffraction (XRD) revealed that rocks are composed of Quartz, Albite, K-Feldspar, Ca- Amphibole, Epidote, Biotite, Chlorite and Muscovite, which are typical silicate minerals. Electrical Conductivity (EC) and pH of leachates measured periodically to monitor reaction progress, revealed that the variations of these parameters were influenced by the mineralogical composition of the rocks, reaction time and experimental conditions. The chemical facies of lixiviate samples from the environment saturated in CO2 at 1 bar were consistent with groundwater chemistry from the study area, corroborating the importance of CO2 gas on rock-water interactions. Mass balance calculations carried out on leachates from experiments saturated with CO2 revealed that major cation chemistry were largely a result of the dissolution of Albite, K-Feldspar, Biotite, Ca-Amphibole and Biotite.