Mineralogy, Physicochemical Characteristics and Industrial Potential of Some Residual Clay Deposits within Ekiti State, Southwestern Nigeria

Abstract

Residual clay deposits overlying Precambrian Basement Complex situated at Orin, Igbara Odo, Ikere and Ado Ekiti were investigated using several analytical techniques. Field evidence supported by mineralogical and physicochemical analyses suggests that the kaolinitic clay deposits is a product of hydrothermal and in-situ weathering of aplite, and granite. Kaolinite is the predominant clay mineral of the studied clay deposits with subordinate quartz, potassium iron oxide and aluminium phosphatic minerals. There is localised occurrence of halloysite. The absence of vanadium in the EDS data of rolled into tubes kaolinite sheets of Ado Ekiti clay match up with XRF data. This result trend combined with field observation suggests that clay bodies formed from weathering of feldspar is deficient in vanadium. The study suggests that morphology of kaolinitic minerals is influenced by the kind of parent material (i.e. feldspars or micas) and degree of chemical weathering. The pH values of pore water from clay samples range from 7.14 - 9.08. The electrical conductivities (EC) of the clay/water slurries (S/L ratio) range from 0.004mS/cm – 3.02mS/cm.  The oxidation reduction potential (ORP) values range between -62.4 and – 6.8 for the solids or slurries prepared with water. The dissolved oxygen (DO) values range from 6.73ppm – 7.26ppm for solids or slurries prepared with water. The loss on ignition ranges from 2.24-13.39. The SiO₂/Al₂O₃ molar ratio of 1.40 and 1.50 for Orin and Ikere clay bodies indicated that a 1:1 clay mineral was the dominant component. The high chemical index of alteration (CIA = 77.97~98.64) and chemical index of weathering (CIW = 97.21~99.93) values probably indicated the complete weathering of feldspars to kaolinite. The weathering index of Parker (WIP) values grouped the analysed clay samples into moderate to intense degree of weathering. This observation is confirmed by the absence of detrital feldspar in the XRD spectra peak. Factor analysis showed enrichment and depletion of major and trace elements which could be attributed to moderate to intense leaching conditions of the presumed parent material. The data shows explicit relationship between the clayeyness value (Al₂O₃/SiO₂ ratio), the relative base loss (RBL) and the cation exchange capacity (CEC). Cluster analysis of major and trace elements showed two groups of chemical differences amongst the elements in the clays; moderate and intense degree of weathered clays. Nevertheless, the variations in the degree of weathering or leaching process have greater contribution to clay deposits differentiation. Assessment of the industrial potential of the studied clay bodies based on their physical and chemical characteristics revealed that they are suitable for the production of refractory bricks and ceramics. Suitable processing would be compulsory if they are to meet the requirements for other industrial applications, such as rubber, paper, paint, cosmetics, and fertilizer industries.

Keywords: Clay; Mineralogy; Physicochemical characteristics; Weathering indices; Pore water; Multivariable analysis; Igbara Odo Ekiti; Ikere Ekiti; Ado Ekiti.