The separation of the chromium(III) dissolved in a tanning wastewater was studied by means of precipitation with calcium carbonate, reverse osmosis with polyamide membrane and adsorption on activated carbon. All tests were carried out at laboratory scale with a wastewater obtained from a unique typical tannage process. In a first stage, the original effluent was treated by sieving and ultrafiltration to perform a partial removal of fats and denaturalized proteins. The separation of chromium(III) by precipitation, reverse osmosis and adsorption was performed with the tanning wastewater so treated. The precipitation efficiency was determined by taking into account the chromium(III) content of the supernatant with the reaction time and with the alkali amount added. The polyamide membrane behavior used was established by the permeate flux and by the rejection of each species. The adsorption valuation involved the determination of the adsorbed amounts of chromium(III), sodium, chloride and sulfate. Under optimum conditions established for each process, the following results were obtained: a supernatant with less than 3.0 mg L-1 of chromium(III) by precipitation, a permeate with less than 2.0 mg L-1 of chromium(III) by reverse osmosis and an equilibrium solution with less than 6.0 mg L-1 of chromium(III) by adsorption. To conclude, the main physicochemical characteristics of the three processes used to remove chromium(III) dissolved in the industrial effluent were analyzed.

A adsorção de ácido sulfúrico em esmectita de soluções aquosas ácidas é estudada. As concentrações de cátions dissolvidos em cada solução em equilíbrio foram determinadas por análise química. As esmectitas original e após cada teste foram simultaneamente caracterizadas por infravermelho, difração de raios X e índice de crescimento. Os resultados obtidos permitiram determinar que as substituições dos cátions de troca e o ataque químico ocorreram em diferentes concentrações de ácido e tempos de tratamento. Foi verificado que durante o tratamento em ácido da esmectita foi produzido um dano progressivo da sua estrutura cristalina. Finalmente foram determinadas as influências da substituição dos cátions de troca e do ataque químico no índice de crescimento.

The adsorption of sulphuric acid on smectite from acidic aqueous solutions was studied. The amounts of cations dissolved in each equilibrium solution were determined by chemical analysis. Simultaneously, the original smectite and the smectite after each test were characterized by infrared, X-ray diffraction and swelling index. The results obtained permitted us to determine that the substitutions of the exchange cations and the chemical attack occurred at very different acid concentrations and treatment times. It was established that during the acid treatment of the smectite, a progressive damage of its crystalline structure was produced. Finally, the influences of the substitution of exchange cations and of the chemical attack in the swelling index were determined.