Comparative study of mineralogy and geochemical compositions of commercially imported bentonite and some locally derived bentonitic clays from Anambra Basin, Southeastern Nigeria

The study focused on the mineralogy and chemical properties of the bentonites recovered from the geological units of the Imo Shale and Ameki Formation, compared with commercially imported bentonite (CIC), for its suitability in the formulation of drilling mud. About 50 suspected bentonite clays were investigated, and properties of starting materials such as pH, conductivity, composition, grain size, degree of alteration, and filtration conditions were utilized during screening. The CIC and four samples that met the API specification for drilling mud were subjected to X-ray diffraction (XRD) and X-ray fluorescence (XRF) analyses. The kaolinite-type consists of 55 % kaolinite, 20 % quartz, 15 % K-feldspar, and 10 % hematite. The smectite-type range from 28-47 % kaolinite, 26-32 % quartz, 12-20 % nontronite. The CIC consists of 12 % quartz, 10 % K-feldspar, 12 % calcite, 41 % nontronite, and 25 % amorphous materials. The SPL15 is predominantly kaolinite, whereas SPL6, SPL8, and SPL11, including the CIC, are smectite-type with a significant amount of kaolinite, except the CIC. The XRF results, show Al2O3 (15.77-25.49) wt%, Fe2O3 (6.61-10.01) wt%, SiO2 (51.67-59.11) wt%, and loss on ignition (7.57-11.22) wt%. Nontronite, one of the smectite group of minerals, was identified from the XRD data. These were supported by elevated concentrations of Fe in some of the samples. More silica may be present in an amorphous phase in the CIC. Palygorskite and basanite are also present in some of the clays. The smectite-type contained an elevated Fe/Al ratio and is rich in Ca-smectite, which differs significantly from the CIC. Based on these results, the primary criteria for the formulation of drilling fluid, using mineralogy, and chemical compositions are achievable. A comparison with the processed CIC has revealed significant levels of compositional disparity/deficits in the local clay. Consequently, treatment/beneficiations with some additives may be necessary to achieve the desired compositions.