The aim of the project is to develop new electrodialysis and electro-electrodialysis membranes, and the necessary associated industrial equipments, adapted to the concentration of acids and their separation from metallic cations. The membranes will be achieved by radiochemical grafting technology and the equipments improved to allow operations in contact with aggressive industrial fluids.
1 - NEW MEMBRANES DEVELOPMENT
Membranes have been realised by grafting monomers on previously beta irradiated films. The supports have been selected among the fluorinated polymers because of their ability to withstand aggressive chemicals.
Numerous membranes have been synthesized using different monomers, cross linking levels and functionalizations. Their properties have been evaluated and the best of them selected for laboratory pilot scale tests.
2 - ELECTRODIALYSIS TESTS
Electrodialysis tests performed with newly developed laboratory pilots, associating the new cationic CS05 and AW anionic membranes. The tests have confirmed the good properties.
SULPHURIC ACID PURIFICATION
E.D laboratory pilot scale tests on an ARA 14/10 and CS83 membrane stack have been conducted on an industrial effluent from a battery manufacturer. The objective was to obtain a 98 g/l sulphuric acid solution containing less than 10 p.p.m of metallic pollutants in order to recycle it in the process.
A three square meters stack of these membranes has been tested together with a new E.D pilot for final evaluation and results have confirmed the laboratory scale results.
Other contacts with a potential end user has lead to an external independent evaluation programme which included measurements of the CS membrane performances in comparison with other new membranes recently on the market.
The evaluation was on the recovery and purification of sulphuric acid, the checking of the reproducibility of the results on several different manufacturing batches and a 300 h aging.
Tests have been conducted with the new AW membrane, in replacement of the ARA previously selected, on an E.D pilot fitted with 15 cells of 16 x 24 cm. Testings have reached the final laboratory stage and as results are very encouraging, new tests on a large pilot are about to start.
Tests have been conducted on an effluent from the Zinc refining industry containing 175 g/l of sulphuric acid polluted with 8,3 g/l of magnesium, 8,3 g/l of zinc and 4 g/l of manganese.
During the different trials an average of 66% of the acid has been recovered with a pollution of less than 1% of the divalent ions contained in the diluate.
This effluent is until now neutralized and precipitated with calcium hydroxide and the precipitates evacuated towards a decantation area. E.D with the new membranes would allow a drastic diminution of the volume of precipitates and an important acid saving.
3 - ELECTRO-ELECTRODIALYSIS
Electro-Electrodialysis tests were performed on two new laboratory scale pilots designed and constructed during the programme. Two types have been constructed, i.e one with open cells and a second type with closed cells. Using the ARA 14/10 membrane, these new equipments have allowed to reconcentrate sulphuric acid from 3 to 13 N. Sulphuric acid purifications from mixtures of metallic salts by cathodic electro-deposition have also been performed with success as well as the purification of a 1 N nitric acid solution containing a 1N concentrated zinc nitrate pollutant but in this last case the AW membrane was preferred.
4 - MEMBRANE CHARACTERIZATION
Collaboration with universities has allowed to improve the knowledge of ions and water transport mechanisms through the membranes.
5 - NEW EQUIPMENTS
New E.D and E.E.D laboratory pilots, designed and constructed during the programme, have allowed to explore the best working parameters for each of the membranes and acids under test. These equipments have been specially designed for the aggressive acid media, they alow a first laboratory evaluation of new processes.
A larger pilot for on site tests has also been developed. Its design was specially studied to make it very compact and allows an easy installation in factories. Results on this industrial pilot have confirmed the laboratory scale results.
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