Lead removal by ThioOctolig

Octolig, a commercially available (a polyethylene diamine covalently attached to silica gel), was subjected to modifications to incorporate sulfur for enhanced removal of lead ion from aqueous solutions. The basic approach was attempted formation of "ThioOctolig" by the reaction of Octolig with thioacetamide in toluene using a shaker bath for 24 or 48 h or in the presence of 10% HCl (1 h). Our experience was that conversion was limited to about 20% based on sulfur analysis for 24 or 48 h reaction time, or in the presence of 10% HCl. In fact, with acidification, the results were poorer. Duplicate runs indicated consistent results. Literature reported that SbCl₃ was an effective catalyst with a reaction time of 1 h. Use of this reagent (1-h reaction time) produced a bright orange red product, in contrast with previous yellow-colored products. A control run indicated that this reagent reacted with Octolig in toluene (in the dark) to produce a red-colored sample; thioacetamide reacted to produce a yellow sample. Use of SbCl₃ (∼5 mole %) did not enhance the sulfur content of Octolig. A sample of Octolig removed 68% lead ion from a 120 ppm aqueous lead while a sample of ThioOctolig (10% S) removed 99.4% lead ions. We also investigated enhancing the sulfur incorporation upon raising the reaction temperature with thioacetamide.