Extraction of Alumina from Kaolin found in Gem Mining Sites of Sri Lanka

Abstract

Kaolinitic clay deposits, esteemed as valuable mineral resources in Sri Lanka, are widely distributed throughout the country. Clay deposits in the Ratnapura District are often unearthed during gem mining operations. Unfortunately, excavated deposits are frequently disposed of openly on the ground without undergoing any value-addition process. This practice alters the soil condition of the vicinity, as the clay soil blocks the gravitational flow of rainwater. This environmental impact can be overcome by adding commercial value to these kaolinitic clay deposits. The present study aims to demonstrate the feasibility of extracting alumina from kaolinitic clay found at gem mining sites and to evaluate the potential of the extracted alumina as an adsorbent. Kaolinitic clay samples were collected from a gem mining site in the Ratnapura District. First, kaolin was transformed into metakaolin through calcination, and then alumina was extracted from the metakaolin via acid leaching using HCl as the leaching agent. Aluminum ions were separated from the leaching solution as Al(OH)₃ using NaOH as the precipitant. The precipitated Al(OH)₃ was transformed into alumina by calcination. The adsorption properties of the extracted alumina were evaluated using methylene blue solution as the adsorbate. Kaolin, extracted, and commercial alumina samples were characterized using XRD, XRF, FTIR, and SEM analysis. XRF analysis revealed that kaolin consists of 29.11 % alumina by weight, and the purity of the extracted alumina was 90.03%. The crystalline phase of extracted alumina was identified as the γ phase via XRD analysis. Extracted and commercial alumina exhibited similar trends in the adsorption of methylene blue under varying adsorption parameters. Accordingly, γ-phase alumina with a purity exceeding 90% can be produced from the kaolinitic clay found at the gem mining site under these experimental conditions. The extracted alumina has demonstrated potential for use as an adsorbent, exhibiting compatibility with commercial alumina.