Recycling of aluminum and caustic soda solution from waste effluents generated during the cleaning of the extruder matrixes of the aluminum industry

• Published in: Journal of hazardous materials Vol. 187; no. 1-3; pp. 459 - 465
• Main Authors: Tansens, Pieter, Rodal, Alberto T., Machado, Carina M.M., Soares, Helena M.V.M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 15.03.2011; Elsevier
• Subjects: Alumina hydrate; aluminum; Aluminum - chemistry; Aluminum base alloys; Aluminum hydroxide; Anodising; Applied sciences; Byproducts; Caustic soda; Chemical engineering; Chemical Industry; cleaning; Conservation of Natural Resources; Effluents; Exact sciences and technology; Filtration; Fourier transform infrared spectroscopy; General purification processes; industry; iron; Liquid-liquid and fluid-solid mechanical separations; neutralization; Pollution; Recovering; Recovery; Recycling; Sodium hydroxide; Sodium Hydroxide - chemistry; Spectroscopy, Fourier Transform Infrared; sulfuric acid; Thermogravimetry; viscosity; washing; wastewater; Wastewaters; Water treatment and pollution; X-Ray Diffraction; Wastewaters; Anodising; Recycling; Recovery; Aluminum hydroxide; Viscosity; Extruder; Filtration; Reaction product; Thermogravimetry; Purity; Liquid waste; Washing; Cleaning; X ray diffraction; Waste water; Dilution; Pollution; pH; Fourier-transformed infrared spectrometry; High purity
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2011.01.048

Anodising industries use a concentrated caustic soda solution to remove aluminum from extruder matrixes. This procedure produces very alkaline effluents containing high amounts of aluminum. The work reported here was focussed on recycling aluminum, as aluminum hydroxide, from these effluents and regenerating an alkaline sodium hydroxide solution. Briefly, the method comprises a dilution step (necessary for reducing the viscosity of the effluent and allowing the subsequent filtration) followed by a filtration to eliminate a substantial amount of the insoluble iron. Then, sulphuric acid was added to neutralize the waste solution down to pH 12 and induce aluminum precipitation. The purity of the aluminum salt was improved after washing the precipitate with deionised water. The characterization of the solid recovered, performed by thermogravimetric analysis, Fourier transform infrared spectroscopy and X-ray diffraction, indicated characteristics typical of bayerite. The proposal method allowed recovering 82% of the aluminum present in the wastewater with high purity (99.5%). Additionally, a sufficiently concentrated caustic soda solution was also recovered, which can be reused in the anodising industries. This procedure can be easily implemented and ensures economy by recycling reagents (concentrated caustic soda solution) and by recovering commercial by-products (aluminum hydroxide), while avoiding environmental pollution.