Characterization of Tannery Wastewater and Detoxification Potentials of Polysiloxane Immobilized Ligand Systems on Selected Heavy Metals

Tanning industry has the highest toxic intensity per unit out- put and requires large amount of water, during tanning chemicals are added per ton of hides such as acids, alkalis, tannins (natural or synthetic), solvents, sulphides, dyes, surfactants, heavy metals (chromium salts), and other auxiliaries. Not more than 20 % of the chemicals are absorbed by leather; the remainder flows out with the effluent and mixture of many compounds may complicate the wastewater treatment such as. Tannery effluent samples were collected at Challawa Industrial Area in Kano and characterized as follows (mg/l): total dissolved solids 7525 ± 620; total suspended solids 3963 ± 816; chemical oxygen demand 6847 ± 1721; biochemical oxygen demand 2906 ± 115 while, pH 7.8 and temperature 28 ± 1 (o C) were recorded respectively. The effluent contained the following concentrations in ppm: Cr3+ (144.344), Fe3+ (49.420), Cu2+ (1.076), Pb2+ (1.766) and Zn2+ (0.238) respectively. Conventional methods used in the tannery wastewater treatments have limitations such as production of toxic sludge and inability to remove heavy metals at trace level. This prompted the use of polymeric modified surfaces with excellent thermal, mechanical and chemical stability properties such as polysiloxane immobilized with ligands as a recyclable extractants for heavy metals. These immobilized ligand systems were synthesized directly by sol gel/chemical modification namely: Polysiloxane Immobilized Thiosalicylic Acid Ligand System (PITSLS), Polysiloxane Immobilized Thiolactic Acid Ligand System (PITLLS), Polysiloxane Immobilized Mercaptoethanol Ligand System (PIMLS), Polysiloxane Immobilized Thiosalicylic-Thiolactic Bi-Ligand System (PITSTLBLS), Polysiloxane Immobilized Thiosalicylic-Mercaptoethanol Bi-Ligand System (PITSMCBLS), Polysiloxane Immobilized ThiolacticMercaptoethanol Bi-Ligand System (PITLMCBLS) and used in their pure and regenerated matrices for detoxification of raw and buffered tannery wastewater. The results obtained shows that they have good adsorption potentials for the selected heavy metals and can be used in the tannery for detoxification process.