Equipment planned and developed by researchers from the State University of Campinas (Unicamp) for recovering metals found in water used in galvanizing processes (a system of metal plating for automotive parts and costume jewelry, for example) has resulted in less final waste, in the form of sludge in this water. Furthermore, there was a substantial saving of water used in the cleaning baths. “An electro-chemical process transforms the metal waste into metals once again”, says Christiane de Arruda Rodrigues, a professor at the School of Chemical Engineering at the Federal University of São Paulo (Unifesp), Diadema campus, and coordinator of the project that is funded by FAPESP in the Technological Innovation in Small Companies (Pipe) modality. The equipment was developed at the School of Mechanical Engineering (FEM) at Unicamp, in a partnership arrangement with Super Zinco from Campinas.
The project started when the company consulted the university in 1999 to find out whether there was any technology for removing metals from the water used in the baths. “As Professor Rodnei Bertazzoli, from FEM, had been developing a project along these lines since 1997 and I, too, was involved in building equipment on a pilot scale, we decided to go in with Pipe to evaluate whether the process was viable for this particular industry”, reports Christiane. The results showed that it was possible. At the time the company had very high levels of heavy metals, of up to 1 gram per litre. After changes in the industrial process the concentration of metals dropped to some 100 mg per litre. “With this amount, the process became viable for the technology we had developed”, says the researcher.
Initially, the test was carried out with equipment in the water used for washing copper, which is easier to monitor. Subsequently, the researchers concluded that it would be necessary to install four pieces of equipment, one for each metal part deposited during the metal plating process. Electro-deposit processes start with nickel. Then the part is placed in water to remove excess metal. The next step is copper-plating, followed by another bath. The part is then nickel-plated, followed by yet another bath and finally it is chrome-plated.
In the traditional process, the running water is clean when it enters and contaminated by metals when it leaves. At the end of the process a sort of broth is left over, which turns into sludge once its volume is reduced. “The planned equipment works like a filter that retains the metal”, explains Christiane. It basically has anodes and cathodes, which are electrodes with a positive and negative charge that make a battery work, for example. It also has a polymeric membrane that helps in optimizing the process.
The anodes are titanium plates covered with precious metallic oxides and the cathodes are porous carbon sponges that are excellent electricity conductors. “The vitreous carbon sponge works like a negatively charged surface to attract the copper and nickel ions (elements that lose electrons) and retain them”, says Christiane. As the water passes through this sponge, the metal sticks to it. “With the electro-chemical treatment there was a saving of 46,000 liters of clean water in just one of the washing tanks.”
Production of equipment for the electrochemical removal of metallic ions from watery effluent (nº 00/12754-0); Modality Technological Innovation in Small Companies Program (Pipe); Coordinator Christiane de Arruda Rodrigues – Unicamp/Super Zinco; Investment R$ 342,999.98 (FAPESP)