Synthesis Of Alumino-Phosphates From Bones For Use In Water Remediation

ABSTRACT

More than two thirds of the earth is covered by water however, only 2.5% of all the water on earth is fresh. In Kenya, only 1.9% of land coverage is occupied by water, with more than 41% of the population lacking access to clean drinking water. A major risk arises from consumption of water containing high levels of fluorides or that contaminated with heavy metals. Conventional technologies such as reverse osmosis, ultra filtration and electro dialysis used in water remediation are efficient but expensive. Greater attention has been given to alternative technologies such as biosorption for water remediation. The present work aimed at hydrothermal synthesis of aluminophosphates molecular sieves adsorbent.Characterization was done using fourier transform infrared spectroscopy. Batch experiments were carried out to determine the effect of initial ion concentration, pH, contact time, temperature, shaking speed, co-ions and adsorbent dose on adsorption process. Adsorption kinetics was done using pseudofirst order and pseudo- second order equations. Isotherm adsorption models were used to analyze the experimental data. The adsorption data for AlPO4 fit very well to the Langmuir model for lead (II) and cadmium (II) ions, which indicated presence of a monolayer adsorbent. The maximum sorption capacity was 6.329 mg/g for lead (II) ions and 5.208 mg/g for cadmium (II) ions at 45 1 oC. A pseudo-second order model described the kinetic data. The initial ion concentrations have significant effect on the adsorption efficiency of the molecular sieves. The highest percentage adsorption occurred at initial ion concentration of 6 mg/L for fluoride ions. Adsorption increased with increase in initial ion concentration for both lead (II) and cadmium (II) ions. The adsorption for fluoride ions, lead (II) ions and cadmium (II) ions also increased with an increase in the AlPO4 dosage and equilibrium reached at 1.00 g/ 100 ml for all adsorption experiments. The optimum pH was found to be between 5 and 7. Temperature variation played an important role in ion adsorption by the AlPO4 molecular sieves. The amount of lead and cadmium (II) ions adsorbed increased from 84.50% to 89.25% and 79.50% to 83.17% respectively, when the temperature was increased from 25 to 45 1 oC. Defluoridation experiments showed increased adsorption from 77.67% to 78.50% as temperatures were raised from 20 to 30 1 oC. Further increase in temperature resulted to reduced percentage of ion adsorption in all experiments. The optimum shaking speed for both lead (II) ions and cadmium (II) ions was 6 revolutions per second. Optimum contact time was found to be 90 minutes. Other anions were found to affect adsorption of fluorides. The results of this work indicate that the alumino-phosphate (AlPO4) molecular sieves constitute a promising material for the development of an adsorption technology for the removal of lead (II), cadmium (II) metal ions and fluoride ions from aqueous systems.