Mineralogy and BCR sequential leaching of ion-adsorption type REE: A novelty study at Johor, Malaysia

Abstract

Since year 2010, advance research in resource investigation, mineralogy and geochemistry, environmental impact as well as processing technique of ion-adsorption type rare earth elements (REE) deposit particularly in mining industry has been conducted worldwide. Ion-adsorption type REEs are formed by weathering process of igneous rocks (typically granites) that contain certain REE-bearing minerals. Effect of the rapidly weathering, REE minerals are decomposed, and ionized REEs are absorbed on clay minerals such as kaolinite and halloysite. A research study has been made in discovery the ion-adsorption type REE prospecting in Johor, Southern Peninsular Malaysia with three vertical weathering profiles (up to 11 m) sampled on Besar island, Tengah island and Hujung island. Parent granite is A-type consist of quartz, K-feldspar, plagioclase, biotite and 0.6–1.4 wt% accessory minerals (zircon, apatite, monazite-(Ce) and chlorite). The main REE-bearing minerals are monazite-(Ce), apatite, zircon, titanite, allanite-(Ce) and bastnaesite-(Ce). Total REE concentrations in raw saprolite (potential REE horizon in weathering profiles) is ranging between 1167 and 2339 ppm. The laboratory leach ability of the REE in different parts of the A-type granite weathering profiles was determined by carrying out a three step BCR sequential extraction procedures. The evidence from the three-step BCR-701 (certified freshwater sediment standard) sequential extraction procedure for ion-adsorption was consistent with a near instant process (≤1 h) with 70–80% recovery rate. This is due to the re-precipitation of REE3+ ions in solution and due to hydrolysis of ions on the clay surface. The ion-adsorption (leached) fraction was enriched in light rare earth elements (LREE) compared with the raw sample compositions of the saprolites and saprocks (Ce/Ce* ratio range largely from 0.17 to 0.82). The LREE accounted for 80–90% of the total REE content in the investigated saprolite and saprock; allowed in agreement with the trend that was observed in Thailand and South China ores.