Adsorption removal of phosphate from aqueous solution by active red mud

Red mud is the waste of alumina industry and has high TiO2 and Fe2O3 content which are active components for the adsorption of anion pollutants. In this study, the uptake of phosphate by red mud activated by heat treatment and acid-heat treatment was investigated. The factors influencing the adsorption were also investigated. The result showed that the red mud sample treated using acid-heat method at 80℃ with 0.25 mol/L HCl for 2 h achieved the highest phosphate removal. For the heat-activated red mud, the sample heated at 700℃ for 2 h preformed better than the other heat treatment. Phosphate removal by the activated red mud was significantly pH dependent, and pH 7 was the optimal pH for phosphate removal. The adsorption fits Langmuir isotherm model well and the maximum adsorption capacities of the acid-heat activated red mud and the heat activated samples were 202.9 mgP/g and 155.2 mgP/g, respectively.

A cleaner two-step synthesis of high purity diallyldimethylammonium chloride monomers for flocculant preparation

In order to improve the flocculation efficiency of polydiallyldimethylammonium chloride（PDADMAC）, high molecular weight PDADMAC should be prepared from high purity diallyldimethylammonium chloride（DADMAC） monomers. In this paper, a cleaner method with microwave irradiation and alkali solidification was proposed for preparing high pure DADMAC by selective heating under low temperature, and the prepared high purity DADMAC is characterized using FTIR and atomic absorption spectrometry. The new method provides a solution to the key technical problem of PDADMAC synthesis. Comparing with the conventional methods, the results showed that the advantages of the novel synthesis include： （a） high purity DADMAC is improved from 57% to 71% ; （b） reaction time of tertiary amine preparation is shortened from 6 h to 7 min; （c） water instead of acetone was used as reaction medium; （d） toxic by-products, wastewater and waste gas are eliminated. Flocculant made from the synthesized high purity DADMAC monomers was proved more efficient in flocculation tests.

Control effects of pε and pH on the generation and stability of chlorine dioxide

A new method, without assistance of activity ratio diagram, was applied to construct the p ε \|pH diagrams for chlorine system. The optimal pH range for generation of ClO_(2) by contacting Cl 2(g) directly with ClO^(-) _(2) solution is within pH 1.35-1.94, particularly within pH 1 35-4 00 only if minimizing the formation of Cl_(2) It is unachievable to synthesize pure ClO_(2) from the reaction of Cl_(2) and ClO^(-)_(2). Conversely, ClO_(2) may be present a variation of stability in different waters owing to the changed p ε and pH. ClO_(2) could be relatively stable if not disproportionate into ClO^(-)_(3), coexisting with ClO^(-) _(2) (p ε 17 63 and pH>9 68), Cl_(2) (pH≤0.92) or Cl^(-)(pH 0.92-9.68). When chlorine system has already reached the ultimate equilibria, ClO_(2) is a stable species in strongly acid media. As the acidity decreases, ClO 2 disproportionates into ClO^(-)_(3) and Cl_(2) Aqueous ClO_(2) is unstable within the normal pH range. This work initially, theoretically elucidates the generation and stability of ClO_(2) by way of the p ε pH diagrams.