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- Ionic interactions in phosphate aqueous solutionsPublication . Ferra, Maria Isabel Almeida; Amaro, Albertina; Mendonça, AntónioMean activity coefficients of NaCl have been calculated, by means of the Pitzer theory,in mixed solutions of NaCl and NaH2PO4 and of NaCl and Na2HPO4, with ionic strength lower than 2 mol kg-1, at 25 ºC. Electromotive force measurements, using a silver, silver chloride and a sodium ion selective electrodes, show nernstian response, in those mixed electrolyte solutions.
- Biological treatment of effluent containing textile dyesPublication . Gonçalves, Isolina Maria da Silva Cabral; Amorim, M. T. P.; Porter, R. S.; Gomes, Arlindo Caniço; Ferra, Maria Isabel; Brás, RuiColour removal of textile dyes from effluent was evaluated using a laboratory upflow anaerobic sludge blanket reactor. Several commercial dyes were selected to study the effect of dye structure on colour removal. The anaerobic reactor was fed with glucose, an easily biodegradable organic matter and selected individual dyes. Results show that some of the dyes are readily reduced under anaerobic conditions even at high concentration of 700 mg/l. The average removal efficiency for acid dyes using this method was between 80 and 90% and that observed for the direct used was 81%. Laboratory experiments using the anaerobic reactor with disperse dyes, such as an anthraquinone based dye, were unsuccessful even at low concentrations of 35 mg/l. Additional experiments were conducted to evaluate the toxicity of a selected disperse dye to an anaerobic environment. Results indicate that the purified dye is more toxic to the biomass than the commercial one.
- Determination of Pitzer parameters for sodium benzoate at 298.15 KPublication . Mendonça, António; Vaz, Margarida; Ferra, Maria I.Sodium benzoate is a salt widely used in industry as preserver. Its activity coefficients in aqueous solutions can be estimated by Pitzer theory, once the necessary parameters are known. Electromotive force (emf) measurements on galvanic cells without liquid junction have been used for the determination o f mean activity coefficients of sodium chloride in the ternary system sodium chloride + sodium benzoate (NaB) + water. Pitzer theory has been applied to this system and those data enabled the evaluation of the specific parameters for sodium benzoate at 298.15 K by linear regression. The values obtained f o r / B(0) NaB and B(1) NaB parameters, respectively 0.177 kg mol-1 and 0.34 kg mol-1 are close to those published already for other carboxylic acid salts.
- Application of the Pitzer theory to the evaluation of pH of the phthalate standard solutionPublication . Mendonça, António; Ferra, Maria I.The pH value of the potassium hydrogen phthalate 0.05 mol.kg-1 has been detemined, using the Bates-Guggenheim convention and lhe Pitzer model for the calculation of the chloride íon activity coefficient. A comparison has been made between lhe two approaches.