Abstract
The aim of the thesis was to examine the potential of synthetic pyroaurite to remove lead(II) from contaminated water. This study was based upon column experiments run in duplicate at room temperature. Heavy metals, many being toxic and bio-accumulative in nature pose a major threat to soil water environment and human health. Lead(II) is among one of the environmental pollutant which is known to be toxic to human health if present in significant amount in waters. To remove such toxic metals from waters, many methods have been developed. The same problem has been addressed in this study. A low cost Mg and Fe based carbonate hydroxide i.e. pyroaurite was synthesized in the laboratory and the removal of Pb2+ from Pb(NO3)2 solution by sorption was investigated. This was done by performing column experiments. The prepared synthetic material was characterized first using XRD and SEM to observe the composition and crystal structure of the material. Poorly crystallized material was formed in the laboratory while presence of a pyroaurite-like compound was confirmed by XRD analysis. The fine-grained synthesized material was mixed with a natural sand to improve the flow properties of the packed column. A solution of 5.8 ppm Pb(NO3)2 was pumped through the column at a rate of 1.25 ml/hr. The effluent was sampled with every 20 or 30 minutes. The two duplicate experiments were run respectively for 8 and 22 days. The concentration of Pb2+ was analysed in the effluent using ICP-MS. Very low concentration of lead(II) was detected in the outlet samples as compared to the incoming Pb(II) concentration into the column, revealing that most of the lead(II) is captured inside the column. On the average 99% of the injected Pb(II) was removed. The effluent concentration was well below recommended drinking water standard by World health organization (WHO).The reacted solid column material was analysed by XRD and SEM. The XRD examination did not reveal presence of a secondary Pb-phase in the reacted samples due to traceable amounts of Pb(II) inside the column material. On the other hand, SEM analysis revealed the presence of Pb(II) in few samples from reacted material. The appropriate mechanism of sorption by which lead(II) is taken up by pyroaurite-like material is not clear, though adsorption and precipitation are considered to be the major mechanisms. iv It is suspected that major part of lead(II) is precipitated on the synthetic pyroaurite material, as Pb(II) was found in the form of small particles in some of the samples examined. Some traces of lead(II) may also be scavenged by adsorption, but no desorption experiments were carried out to verify it. The results indicated that the precipitates were formed either as lead carbonates or lead oxides. Observations and calculations have showed that about 99% of Pb(II) is taken up by pyroaurite-like material. The results suggested that synthetic pyroaurite has potential to remove Pb2+ from aqueous solutions and therefore can be a good candidate for the purification of contaminated waters.