EPMA characterisation of strüverite from amang of Peninsular Malaysia

Abstract

The heavy minerals from tin tailings or amang comprises a wealth of minerals which contain some of the most sought after metals in industry that includes tantalium and niobium, which are widely used in the computer and cellular phone industry because of their high reliability, high melting points and corrosion resistance characteristics. An extended investigation was carried out on the EPMA (Electronprobe Microanalyzer) into the complex nature of struverite, the source of tantalium (Ta) and niobium (Nb) in amang, in particular its complex mineralogy, chemistry and associated phases/ minerals. EPMA data of struverite show that it is a complex intergrowth of rutile (TiO 2 ), tantalite (Ta 2 O 5 ) and columbite (Nb 2 O 5 ) with only very few grains devoid of any inclusions or exsolved phases. EPMA analysis of three pure struverite grains, devoid of intergrowths, gave consistent ratios of Ti (19.58-29.08 wt%), Nb (5.45-7.99 wt%), Ta (25.43-33.46 wt%) and Fe (6.89-8.11 wt%). They also contain significant amounts of Sn (0.79-2.62 wt%) and Th (3.25-6.03 wt%) but very low W (0.11-0.47 wt%) and Mn (0.01-0.12 wt%) and no Y. Other struverite grains which have inclusions or exsolved phases or intergrowths, all show very variable contents of Ti, Nb, Ta, Fe, W, Mn, Th and Y. BSE (backscattered secondary electron) images on the EPMA also picked up zoned struverite crystals where great variations in compositions are clearly discernible in X-ray maps of these zoned crystals. EPMA analysis of fusion discs of struverite concentrates from amang also show quite variable contents for Ti (12.60-54.38 wt%), Nb (1.71-13.12 wt%), Ta (2.88-7.40 wt%), Fe (1.43- 15.65 wt%), W (0-3.48 wt%), Mn (0.05-1.51 wt%) and Th (0-29.76 wt%). The presence of Th with or without Y in some struverite grains could be a useful criteria for determining their source area. Knowledge of the complexity of struverite is useful in configuring the correct recovery processes for Ta and Nb. particular its complex mineralogy and chemistry under the electronprobe microanalyzer or EPMA. The paper describes the complex nature of struverite and the various phases/minerals associated with it. The composition of these various phases/minerals and their possible origins or source areas are also discussed.