Experimental weathering of carbonate rocks, Pérolas Cave, Iporanga (SP)

Abstract

Experimental studies were performed to study the chemical weathering of carbonate rocks from the Pérolas Cave, Iporanga municipality, State of São Paulo. Soxhlet extractors were used to accelerate the leaching process in two different ways: continuous and intermittent. The leaching solution obtained from the continuous test was chemically analyzed at the end of the process (about 454 hours), and the precipitates were separated and mineralogically analyzed by X-ray diffraction (XRD). In the intermittent leaching process, solutions and precipitates were collected after a predetermined period of time and chemically analysed to determine the number of ions removed from the weathered rocks. It was found that the ions mainly leached in the beginning of the experimental weathering were Na+ and Mg2+; however, when the leaching process was accelerated, Sr2+, Ba2+ and Ca2+ became the most remobilized ions, along with Na+, leading to the precipitation of calcite. In the continuous leaching test, it was observed that the concentrations of Sr2+ and Ba2+ were lower compared to the intermittent test, showing that these ions were probably co-precipitated with calcite. The low Mg/Ca ratio in the experimental leaching solutions may have caused the precipitation of calcite instead of aragonite. It was noted that there was a higher rate of remobilization of the constituents of the carbonate rocks on the level where the samples were subjected to fluctuations of the water table in the compartment of the Soxhlet equipment. Kaolinite is the main secondary mineral in the weathered rock.