Ghassoul – Moroccan clay with excellent adsorption properties

Abstract

Ghassoul, Mg-rich clay consisting mainly of stevensite and containing also additional minerals (sepiolite, quartz, dolomite, gypsum, celestine) is mined in Morocco where the only known deposit in the world is located in Moulouya Valley in Fès-Meknès region. Ghassoul, formed by diagenetic transformation of dolomite in Tertiary fresh-water or brackish-water lacustrine environment, was used for centuries as a natural soap and shampoo. In 1884, the very first scientific report about this material was published by A. A. Damour who provided information about chemical composition of ghassoul. Over the next one hundred years, this material became a subject of geologists' interest until 1998 when the first study focused on practical applications of ghassoul was reported. Between 1998 and 2016, twenty-eight studies were published, twenty-four of which were focused on practical use. According to the studies, the ghassoul can be successfully used as an adsorbent of heavy metals and organic compounds, as a precursor of cordierite ceramics, and, recently, also as a component of functional composites for catalysis or photocatalysis. However, the greatest interest is still in adsorption.This review article is divided into three main sections. The first one provides information about chemical composition, crystallochemical formula, cation exchange capacity, specific surface area, and density of ghassoul. The second and the third section contain data obtained by various authors from experiments on adsorption of heavy metals (As, Cd, Cr, Cu, Hg, Mn, Pb, and Zn) or organic compounds (basic yellow 87, methyl violet, methylene blue, orange G, rhodamine B, metalaxyl, and tricyclazole), respectively. Dose of ghassoul, initial concentration of adsorbate, adsorption capacity, contact time, temperature, and pH are listed in two tables (the first one for heavy metals, the second one for organic compounds). Some of the articles contain tables comparing the adsorption capacity of ghassoul with adsorption capacities of other materials reported elsewhere. Comments on the comparisons are also provided in this article and it is shown that only few materials can compete with adorption capacity of ghassoul.