Comparative analysis of Mukurweini Raw Kaolinite and Alkali Modified Kaolinite as Solid Adsorbents for Removal of Nitrate (\(NO^-_3\)) and Phosphate (\(PO^{3^-}_4\)) from Aqueous Solutions: Effect of pH, Adsorbent Dosage, Adsorbate Concentration and Contact Equilibrium Time
Makani Bungishabaku Rachel
Department of Chemistry and Biochemistry, College of Arts and Sciences, Ohio State University, USA.
Patrick Kimutai Tum
Department of Chemistry, Faculty of Science and Technology, University of Nairobi, P.O. Box 30197-00100, Nairobi, Kenya.
Nyabaro Obed Mainya *
Department of Chemistry, School of Pure and Applied Sciences, Kisii University, P.O. Box 408-40200, Kisii, Kenya.
*Author to whom correspondence should be addressed.
Abstract
Kenya is facing severe water scarcity and pollution challenges driven by population growth, climate change, poor infrastructure, and agricultural runoff, and highlights adsorption—particularly using modified kaolinite—as a low-cost and effective method for treating contaminated agricultural wastewater. The present study investigated the adsorptive properties of Mukurweini raw and alkali modified kaolinite (AKM) for the removal of nitrate and phosphate from aqueous solutions. Two samples of Mukurweini raw ceramic clay each weighing 3 kg was obtained from the Kimathe valley by excavation at a depth of 1 meter using a shovel (grid method). The raw samples were separately calcined at t=700°C in a furnace for 2 hours to promote dehydroxylation reactions within the clay material. One sample of the calcined clay was converted to Alkali Modified Kaolinite by weighing out 50 g of the freshly calcined brown clay material and subsequently modifying using NaOH (v=50 mL; c= 7 mol. L-1) in an orbital shaker under agitation for 30 minutes at a temperature of 60°C to obtain a homogenous paste.
Additionally, samples of calcined raw and alkali modified kaolinite samples were separately placed into a pressure cooker, heated for 3 hours, washed with ethanol, oven-dried at 110°C for 1 hour, and finally activated in a muffle furnace at 700°C for 2 hours. Batch adsorption experiments were designed to evaluate the optimum adsorption parameters i.e. pH, adsorbent dosage, adsorbate concentration and contact time achieved at equilibrium and determine the most efficient clay type i.e. raw and alkali modified kaolinite. Adsorptive efficiencies were determined using laboratory spiked solutions (c=10, 20,50&100 ppm) diluted from a stock solution c=1000 ppm. The average results show 99.2% removal of nitrate (\(NO^-_3\)) and phosphate (\(PO^{3^-}_4\)) from aqueous solutions. The results show Alkali-Modified Kaolinite (AKM) as effective adsorbent compared to raw kaolinite. Alkali-Modified Kaolinite (AKM) adsorbed 99.2 % (\(NO^-_3\)) and (\(PO^{3^-}_4\)) from aqueous solutions. Raw kaolinite shows negligible adsorptive capacity for (\(PO^{3^-}_4\)) and 95.7% removal efficiency for (\(NO^-_3\)). Optimum adsorption parameters were determined; [(pH= 7-; pH=10 -phosphates); (adsorbent dosage= 0.1 g – nitrates/phosphates); (adsorbate concentration of 10 ppm nitrate/phosphates) ;( adsorbate-adsorbent contact equilibrium time= 10 mins – nitrates/phosphates)]. The results show potential application for Mukurweini clay in removal of (\(NO^-_3\)) and (\(PO^{3^-}_4\)) from aqueous solutions.
Keywords: Raw Mukurweini clay, alkali-modified kaolinite, adsorption, \(NO^-_3\), \(PO^{3^-}_4\), aqueous solutions