70|90K
tonnes of waste treated every year
2|3K
tonnes of recovered product returned every year
Tanneries deliver spent baths to the consortium facility by road transport, both in liquid form, either as is or flocculated, and in the form of pressed panels. Each year, the Consortium receives approximately 90,000 tonnes of spent solution with an average chromium content of 0.4%, and is able to recover more than 85% of the chromium delivered, producing a product with an average CrSO4 content exceeding 9–10%.
Once homogenised, the waste is fed into a reactor where the chemical precipitation of chromium takes place (insoluble at alkaline pH), using 50% caustic soda. The precipitated chromium is then concentrated, through two filter-press lines, into solid and dewatered panels.
Once the chromium has been almost completely separated, the refining phase begins. The panel is dissolved again in dedicated reactors with the addition of 97–98% sulphuric acid, producing a chromium sulphate solution. The solution is then mixed with diatomaceous earth, which absorbs any impurities still present. The earth is subsequently separated through a second filter press (polishing stage).
The pressing process produces a stream of liquid basic chromium sulphate, which is stored in tanks (batches) and analysed. Only after a positive result from the laboratory, which certifies its quality according to a specific technical data sheet, can the product be returned to production sites for reuse within the tanning cycle.
Santa Croce sull’Arno (Pisa)
Via del Bosco, 283
Transparent Administration
Consorzio Aquarno spa Registro Imprese PISA P.IVA e Cod.fisc. 00857500508 R.E.A. PISA PI026-8385 Capitale sociale € 800.000 i.v.
