![]() In recent years, environmental pollution control mechanism as related to wastewater has become a topical issue among environmentalist owing to its negative influence the pollutants on human 4. It is obvious that tannery wastewater represents an important source of environmental contamination and delay in treatment can lead to different health challenges since it is toxic and contain several non-biodegradable constituents. Also, Fe exists in several oxidation states such as + 2, + 3, + 4 and + 6 and exposure to wastewater containing a high concentration of Fe can result in chronic fatigue, joint pain, diabetics mellitus, heart attack, and liver disease to mention but a few 3. The Cr(VI) can easily bioaccumulate along food chains and eventually result in biomagnifications and therefore become a major threat to human and aquatic species 2. Exposure to wastewater containing Cr(VI) can lead to dermatitis, occupational asthma, eye irritation, kidney and liver damage, lung cancer, respiratory irritation pulmonary congestion, oedema, skin irritation amongst others. Cr (III) is regarded as an essential trace element while Cr 6+ has been reported to be more toxic to animals and non-essential than Cr 3+ due to its high solubility in water and soil 1. One of the major heavy metals present in tannery wastewater is chromium and exists in two different forms trivalent (Cr 3+ or Cr(III)), and hexavalent, (Cr 6+ or Cr(VI)). Most of the chemicals used during pre-tanning and tanning operations include lime, ammonium sulphate, sodium chloride, chromium sulphate, sulphuric acid and sodium bicarbonate. Specifically, industrial tanning process which transforms animal hides and skins into leather generate highly turbid, coloured and foul-smelling wastewater containing different organic and inorganic pollutants especially chromium complex collagens, sulphides, chlorides, hydrogen sulphide, which have become threats to human and need to be addressed. Industrial manufacturing processes utilize a high amount of clean water during operations and at the same time generate and discharge a large volume of untreated wastewater into water bodies. The ZnO/clay nanocomposites exhibited excellent recyclable and re-useable properties even after six repeated applications and can, therefore, be applied in wastewater treatment for removal of heavy metals and other physicochemical parameters.Įnvironmental contamination via natural and anthropogenic activities have been recognized as one of the major global problems confronting the human race and aquatic species. The thermodynamic parameters such as enthalpy change showed that that adsorption of metal ions and other parameters was feasible, spontaneous and endothermic. The mechanism for the adsorption of metal ions in tannery wastewater onto the nano-adsorbents was examined using Weber Morris intra-particle diffusion model and Boyd plot which showed that the adsorption process was both intra-particle and film diffusion controlled. It was found that the Jovanovic isotherm model fitted the adsorption experimental data most with the highest correlation (R 2 > 0.99) for both nanoadsorbents and indicate the occurrence of adsorption on monolayer and heterogeneous surfaces. The kaolin/ZnO nanocomposites exhibited better adsorption performance than kaolin due to higher surface area of the former than the latter. ![]() While 78% Cr(VI), 91% Fe(III), 91% COD, 89% BOD and 73% Chloride were removed by kaolin under the same conditions. The maximum removal of Cr(VI) (100%), Fe(III) (98%), COD (95%), BOD (94%) and Chloride (78%) was obtained at 15 min by kaolin/ZnO composites. Batch adsorption studies were carried out by varying the parameters such as contact time, adsorbent dosage and temperature. ![]() BET measurement showed an increase in the surface area of kaolin/ZnO nanocomposites (31.8 m 2/g) when compared to kaolin (17 m 2/g). The HRSEM/EDS/XPS analysis confirmed successful immobilization of clay structural network on the lattice layers of zincite hexagonal structure of ZnO nanoparticles. The prepared adsorbents were characterized using different analytical tools such as X-ray diffraction, Fourier transforms infrared, high-resolution transmission electron microscopy, energy dispersive spectroscopy, selective area electron diffraction and Brunauer Emmett–Teller (BET) and X-ray Photoelectron Spectroscopy (XPS). ZnO nanoparticles and kaolin/ZnO nanocomposites were prepared by sol–gel followed by wet-impregnation methods. In the present study, comparative studies of kaolin and kaolin/ZnO nanocomposites for the adsorption of Cr(VI), Fe(III), COD, BOD, and chloride from tannery wastewater were investigated.
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