Improper disposal of untreated wastewater into the environment is a common practice in developing nations. This is capable of causing contamination of streams, groundwater, and seawater. With the growing number of industries in Nigeria, there is high risk of exposure of the citizenry to water pollution. This situation can be averted by getting rid of the toxic substances in the industrial wastewater before discharge. This paper assesses the geochemical composition and efficiency of two different natural-grade diatomites in the removal of heavy metals from polluted waters.

The results indicate that the geochemical composition of the diatomite is SiO2 (84.9–85.1%), Al2O3 (8.8–9.0%), and Fe2O3 (2.5–2.8%) with a trace metal composition of Cu (3.1–3.5 ppm), Zn (4.9–5.5 ppm), Pb (0.2–0.5 ppm), and Bi (0.21–0.25 ppm). Adsorption experiments performed under similar conditions for the treatment of Pb- and Zn-contaminated wastewater indicates that the adsorption of Pb by diatomite was best described by the S-type curve isotherm, whereas the adsorption of Zn by the diatomite was indicative of the L-type curve isotherm.

Similarly, light and heavy diatomites adsorbed 42.8% and 48.8% of Pb, respectively, and 38.7% and 34.4% of Zn, respectively. The percentages of lead removal by the diatomites are expressed by the regression equations y = -0.03x + 85.72 (R2 = 0.5569) and y = -0.04x + 83.61 (R2 = 0.6466), while those of zinc are expressed by the regression equations y = 0.04x + 17.38 (R2 = 0.6499) and y = -0.06x + 61.89 (R2 = 0.0682) for heavy and light diatomites, respectively (where y = % removal by the diatomites and x = initial concentration of Pb and Zn in ppm). The diatomites have been found suitable as commercial filter media.