Chromate sorption on pyridine strong base anion exchangers with different functional groups (methyl, ethyl, and butyl groups), at the quaternary nitrogen atoms, was studied as a function of various initial concentrations (100 -1500 mg Cr/L) and counterion type. The studied resins in the Cl Ϫ[ form have higher Cr(VI)-retention capacities than those in the SO 4 2Ϫ form. The pyridine strong base anion exchangers showed a selectivity reversal for the sulfate and chromate anions compared to that of the commercial resins. The alkyl substituent length of the quaternary nitrogen atoms exerted a substantial influence on the Cr(VI)-retention capacity values for the resins in the Cl Ϫ form; the chromate anions preferred resins with methyl functional groups, that is, resins with a greater hydrophilic structure. For the resins in the SO 4 2Ϫ form the length of the substituent at the quaternary nitrogen atom had only a negligible influence on their Cr(VI)-retention values.

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ABSTRACT:The aim of this research work was a thermodynamic and kinetic study of the retention of Cr(VI) ions from a K 2 CrO 4 solution on macroporous weak-and strongbase anion exchangers, Lewatit M 64 A and Lewatit MP 500 A, respectively. Also, the correlations among the ion-exchange rate, the retention capacity of Cr(VI), and some process parameters were established. The parameters studied mainly were the concentration of Cr(VI) ions and the type of the counterions coupled with active groups from the anion exchangers. The results led to the conclusion that, for the Lewatit M 64 A resin, there is the following order of the Cr(VI) retention capacity: RCl Ͼ R 2 SO 4 Ͼ ROH, while for the strong-base anion exchanger, the retention capacity for the Cr(VI) ions is different: ROH Ͼ RCl Ͼ R 2 SO 4 . In the Cl Ϫ form, both anion exchangers have the same retention-capacity values. On the other side, the weak-base anion exchanger in SO 4 2Ϫ and OH Ϫ forms presents the lowest retention-capacity values. The process kinetics also presents some differences: for the Lewatit M 64 A resin, the ion-exchange rate has lower values, especially in the OH Ϫ form. This result is attributed to the increase of the OH Ϫ ion concentration in the solution and its presence hinders the dissociation of the active groups of a weak-base anion exchanger.

An experimental study on 4-chlorophenol (4-CP) degradation with hydrogen peroxide by advanced oxidation process Photo-Fenton type is presented. The oxidation process is determined by the very high oxidative potential of the OH. radicals generated inside the reaction medium by Fe 2+ catalyst coupled with UV radiations. The influence of the hydrogen peroxide excess, initial solution's pH, Fe 2+ catalyst concentration, initial concentration of 4-CP and reaction time on the oxidation process are presented.

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untersucht. I n Schwefelkohlenstoff erhalt man homogene Produkte der Polykondensation, deren Eigenschaften von jenen der Ausgangsverbindungen abhangen. I m allgemeinen sind die Produkte unloslich und schmelzen nicht. Die besten Resultate wurden erzielt, indem man von 1.3-Dichlormethyl-4.6-dimethylbenzol ausging. Die Homopolykondensate wurden mit Hilfe von IR-Spektren charakterisiert.

Les résultats de l'étude du polycondensation du dichloro‐1,2 diphényl‐1,2 éthane (1) avec le benzène, le toluène, le m‐ et p‐xylène, le mésitylène et le tétraméthyl‐1,2,4,5 benzène sont présentés. Les produits de copolycondensation ont une structure tridimensionnelle; ils sont infusibles et partiellement solubles dans le benzène. Le comportement thermique a été analysé par un dérivatograph. Les produits ont été caractérisés aussi par les spectres IR.

Nous avons étudié des réactions de copolycondensation du bis(chloro‐1 éthyl)‐1,4 benzène (1) avec le benzène, le toluène, le m‐ et le p‐xylène, le mésitylène et le tétraméthyl‐1,2,4,5 benzène. Les réactions de copolycondensation étudiées donnent des produits à structure tridimensionnelle (infusibles et seulement partiellement solubles) měme dans le cas de tétraméthyl‐1,2,4,5 benzène où c'était à prévoir d'obtenir un produit linéaire.