Removal of phosphate ions from aqueous solutions using bauxite obtained from Mulanje, Malawi

  • MW Kamiyango
  • SMI Sajidu
  • WRL Masamba
Keywords: Adsorption, bauxite, phosphate, gibbsite, goethite, eutrophication.


Studies on stream water and effluent from selected wastewater treatment plants in Blantyre, Malawi, have reported phosphate concentrations above recommended levels. High phosphate levels in the effluent and streams pose a threat to aquatic life through the stimulation of excessive growth of plants and toxic cyanobacteria. Phosphate removal by bauxite was investigated as a function of pH, contact time, dosage, competing ions and initial phosphate concentration by means of jar tests. Phosphate removal increased with decreasing pH with maximum removal (99.75%) recorded at pH 2.40 ± 0.10. Phosphate removal was attributed to ligand exchange reactions with gibbsite and goethite minerals that are chemically and electrostatically favoured at low pH. Bauxite indicated a high phosphate removal capacity with 98.42% removal recorded for a dosage of 15 g/l. This was attributed to the presence of goethite and gibbsite minerals for which phosphate has a strong affinity. Kinetics studies revealed a fast adsorption reaction with 61 and 65% phosphate removal achieved after 30 min of contact at 20 and 40°C respectively. Phosphate removal was enhanced in the individual presence of calcium and magnesium ions whereas carbonate and sulphate ions reduced it by competing for active sites.

Key words: Adsorption, bauxite, phosphate, gibbsite, goethite, eutrophication.


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eISSN: 1684-5315