Facile purification of locally mined gypsum and its use for preparing nano-hemihydrates

Abstract

Gypsum has a wide range of applications, in interior decorations, building construction, supplements or implants in orthopaedics to mention a few. However, in many developing countries including Nigeria, there is still a large-scale importation despite huge available natural deposits. In this study, a facile method to purify locally-mined gypsum has been explored based on the mineral retrograde solubility in water. The purified gypsum was investigated for its elemental composition in comparison to the crude sample and a commercially obtained medical-grade gypsum using X-ray fluorescence (XRF). The results showed that the purified gypsum contained 94.05% CaSO4 compared with the crude which had a CaSO4 content of 58.10%. Hemihydrates obtained by the treatments of the purified gypsum in an oven, autoclave and microwave gave different morphologies when observed under a scanning electron microscope (SEM). Transmission electron microscopy (TEM) showed that particle sizes of all the hemihydrates were within the range 9 nm to 32 nm, but the microwave-derived sample exhibited the most desirable morphological characteristics which could impart high mechanical performance. We have reported here a new facile method for purifying gypsum ore that can have huge commercial benefits.