Soda and Aluminum Recovery from Spent Etching Baths by Aqueous Precipitation

Abstract:

The aluminum anodising industry is an important industrial sector that produces great amounts of polluted effluents, which after treatment generate sludge. This fact brings environmental and economical concerns to the companies. Best way to deal with the problem, according to the “prevention strategy” set by the European Directive on Integrated Pollution Prevention and Control, is to implement preventive techniques and technologies to optimise the use of resources and minimise losses, and in turn waste. Among the operations of an anodising line, the etching/satinising stage is responsible for the production of a huge quantity of wastewater neutralisation sludge and for the wrong use of caustic soda. “Caustic etch recovery” technology is claimed to drastically reduce the generation of neutralisation sludge and the purchasing of fresh caustic soda by regenerating the exhausted etching/satinising solution, through an aqueous precipitation reaction. This paper presents the capability of the technology to effectively regenerate the exhausted caustic solution, and investigated the parameters with major effect on the process yield, in order to optimise it. It was demonstrated that the technology effectively recovers the solution, increases its soda content and diminishes the dissolved aluminum content by precipitation. Moreover the conditions that optimise the process are simple and inexpensive. After treatment the solution present the properties to be recycled in the etching/satinising operation.

• Periodical: Materials Science Forum (Volumes 730-732)
• Pages: 642-647
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.730-732.642
• Online since: November 2012
• Authors: Andrea Berto, Carlos A. Nogueira, Fernanda Margarido
• Keywords: Alumina Precipitation, Aluminum Anodising, Etching Bath, Soda Recovery

References

[1] Toward an Improved Policy on Industrial Emissions, Communication from the Commission to the Council, the European Parliament, the Economic and Social Committee and the Committee of the Regions, Brussels, 21 Dec., 2007.

[2] Council Directive 96/61/EC of the 24th September Concerning Integrated Pollution Prevention and Control, (1996)

[3] V. O'Malley, The Integrated Pollution Prevention and Control (IPPC) Directive and its implications for the environment and industrial activities in Europe, Sensors and Actuators B59 (1999) 78-82.

DOI: 10.1016/s0925-4005(99)00199-9

[4] M.C. Barros, M.T. Torres, P.M. Bello, E. Roca, J.J. Casares, Integrated Pollution Prevention and Control in the Surface Treatment Industries in Galicia (NW Spain), Clean Techn. Environ. Policy 10 (2008) 175-188.

DOI: 10.1007/s10098-007-0138-z

[5] "Plano Nacional De Prevenção dos Resíduos Industriais (PNAPRI)". Vol. 1, November, 2001.

[6] L.K. Wang, N.K. Shammas, Y. Hung, Waste Treatment in the Metal Manufacturing, Forming, Coating, and Finishing Industries, CRC Press, 2009.

DOI: 10.1201/9781420072242

[7] Woodard & Curran, Industrial Waste Treatment Handbook, Second Edition, Butterworth-Heinemann, 2006.

[8] European Aluminum Association (EEA) – Activity Report, 2009.

[9] Linee Guida sui Rifiuti Speciali – Industria Galvanica, PHARE Twinning Project Ro2004/IB/EN-07, 2007.

[10] E. Álvarez-Ayuso, Approaches for the treatment of waste streams of the aluminium anodising industry, J. Hazard. Mater. 164 (2009) 409-414.

DOI: 10.1016/j.jhazmat.2008.08.054

[11] Eco-Tec's Caustic Etch Recovery System, http://www.eco-tec.com/products/caustic_etch.php (accessed in April 2011)