Abstract
Geophagy clay has been used in tropical regions as gastrointestinal protector for adsorbing toxins in human body, but it was rarely used in adsorbing heavy metals contaminants in water. This study determines elemental concentration of geophagy clay and evaluates its adsorptive capacity in removing Cd2+ and Pb2+ in water. Fifteen clay samples were randomly collected from three layers in the space of one meter apart from Amawom clay deposit in Ikwuano local government, Southeast Nigeria. Elemental analysis was carried out using the inductively coupled plasma mass spectrophotometer (ICP-MS), and chemical characterization was performed with Fourier transform infrared spectroscopy (FT-IR) and X-ray diffractometer (XRD). The adsorptive capacity of Cd2+ and Pb2+ on the clay samples was evaluated using standard solutions of the metal ions. The result of the elemental analysis in mg/kg (Pb ≤ 12.4, Zn ≤ 2.75, Co ≤ 1.50, Ni ≤ 1.47, Mn ≤ 15.0, Cd = 0.01, Ca ≤ 300, Al ≤ 3466, Na ≤ 13.3, and Hg = 0.02; P ≤ 40.0) revealed that the concentrations of most of the studied metals in the three layers are statistically similar and fall below the permissible recommended safety levels. The presence of functional groups (hydroxyl, amine, and carboxylic/ester) and minerals (kaolinite, goethite, and quartz) provided evidence of the good adsorptive properties of the clay samples. The adsorption of Cd2+ and Pb2+ unto the clay samples increased with increase in pH, concentration, time, and temperature, and the equilibrium data for the adsorption fitted well into Langmuir isotherm. The study, therefore, concluded that geophagy clay possesses the capacity to adsorb Cd2+ and Pb2+ for water treatment.
Highlights
Clay properties including high adsorption and absorption capacities, cation exchange capacity, and extremely fine particle size, e.g., smectites and kaolin group minerals and structural/surface properties. ese properties permit their use in removing oils, secretions, toxins, and contaminants from materials. e study of the mineralogical composition of geophagy clay has predominantly indicated the presence of kaolinite with minor palygorskite, nontronite, illite, K-feldspar, halloysite, and calcite [3, 10, 11]
Ikwuano is located between latitudes 5°24′–5°291 N and longitudes 7°32′–7°37′ E. It falls in typical rainforest vegetation in the southeast agroecological zone of Nigeria with typology of the degraded humid forest ecology in the sub-Saharan Africa [13]. e soils are coarse-textured, deep, and well-drained. ey have weak, coarse, and fine crumbs at the epipedon and underlain by moderate subangular blocky structures in the endopedon. e soils are characterized by toposequence and lithosequence and are classified as Ultisols because the base saturation is
E result shows the presence of essential (Ca, Na, and P) and nonessential elements ( Pb, Cd, Al, and Hg), which vary at different layers. e highest mean concentration of Pb, Ni, Co, Fe, P, Al, and Hg was detected at the bottom layer of the clay sample while the minimum values were recorded at the top layer except for mercury
Summary
E study site was a clay deposit located at Amawom in Ikwuano local government, Southeast Nigeria. Ikwuano is located between latitudes 5°24′–5°291 N and longitudes 7°32′–7°37′ E. It falls in typical rainforest vegetation in the southeast agroecological zone of Nigeria with typology of the degraded humid forest ecology in the sub-Saharan Africa [13]. E soils are coarse-textured, deep, and well-drained. Five samples were randomly collected from each layer to make a total of fifteen samples. E collected clay samples were transported to the laboratory where they were air-dried for fourteen days at ambient temperature and pulverized prior to analysis. Preliminary elemental study of the collected clay samples was carried out in duplicate. Total acid digestion with aqua regia (2 ml HNO3 + 6 ml HCl) was carried out, and the concentrations of elements in the digested solutions were measured using an inductively coupled plasma mass spectrophotometer (ICP-MS) (Perkin Elmer Nexion 300 Q ICP-MS)
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