Physicochemical Characteristics of the Middle Triassic Limestone in Ha Nam Province, Vietnam and the Ability of Adsorption of Heavy Metal Ions from Aqueous Environments

Abstract

Calcium carbonate rocks of middle Triassic age formations account for a large amount, up to 25% of Vietnam’s limestone potential. Ha Nam is one of the areas with large reserves of middle Triassic limestone of the Dong Giao Formation, up to billions of m3. Dozens of limestone quarries have been licensed to exploit the area for different applications such as cement, lime, light powder, and common building materials. The research on limestone as a raw material in the treatment of contaminated water is still limited. In this study, the middle Triassic limestone sample (Dong Giao formation) from Ha Nam area is used to determine physicochemical characteristics and then to investigate the ability to remove Pb2+ ions from an aqueous solution. The analysis results show that the limestone in the study area is of good quality. The mineral composition is mainly calcite and the CaO content is up to 92–100%. Other properties of limestone such as physical and radioactive properties indicate that the limestone here can be used safely for different fields. For environmental treatment, different conditions such as contact time, solution pH, adsorbent weight and initial concentration of Pb2+ were tested. The results show that experimental conditions of pH0 = 6.2 and a temperature of 30 °C, with 0.1 g of limestone material and an initial concentration of Pb2+ of 50 mg/L, the Pb2+ adsorption can reach equilibrium after about 40 min and efficiency reached 98.88%. The adsorption process follows the Langmuir adsorption isotherm model with the maximum monolayer adsorption capacity of 76.22 mg/g and follows the pseudo-second-order kinetic equation. The result indicate that unmodified the Triassic limestone powder has a significant potential for the removal of heavy ions from an aqueous solution.