a b s t r a c tIn this work, the inhibitory effect of a commercial anti-scalant (Veolia Hydrex s 9209) on the calcium minerals of carbonate, sulfate and hydrocalumite (Ca/Al) clay deposition from seawater has been investigated. Different concentration factors and anti-scalant doses were studied by analyzing the water hardness and turbidity. The inhibitory effect of the investigated anti-scalant was efficient even at lower concentrations. The percentage inhibition decreases with increasing the temperature and increases with increasing the dose/amount of the anti-scalant. The carbonate scale inhibition was 499% and 98-99% at 50 and 70°C, respectively. The percentage inhibition of sulfate from hemihydrate was ranged from 80% to 87% for 2 and 8 ppm anti-scalant at 50°C. The inhibition of Ca/Al hydrocalumite deposition increases from 70% to 90% upon increasing the dose from 3 to 5 ppm, respectively. A recommended useful dose of antiscalant for seawater is 5 ppm.
Research work on removal of fluoride from water, referred to as water defluoridation, has resulted into the development of a number of technologies over the years but they suffer from either cost or efficiency drawbacks. In this work, enhancement effects of phosphate and silicate on defluoridation of water by low-cost Plaster of Paris (calcined gypsum) were studied. To our knowledge, the influence of silicate on defluoridation was not reported. It was claimed, that the presence of some ions in the treated water samples, was decreasing the fluoride removal since these ions compete the fluoride ions on occupying the available adsorption sites, however, phosphate and silicate ions, from its sodium slats, have enhanced the fluoride % removal, hence, precipitation of calcium-fluoro compounds of these ions can be suggested. Percentage removal of Fby neat Plaster is 48%, the electrical conductance (EC) curve shows the typical curve of Plaster setting which begins at 20 min and finished at 30 min. The addition of phosphate and silicate ions enhances the removal of fluoride to high extent > 90%. Thermodynamics parameters showed spontaneous fluoride removal by neat Plaster and Plaster-silicate system. The percentage removal with time showed second-order reaction kinetics.
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