![]() ![]() Removal of permanent hardness is carried out cold with sodium carbonate which may or may not be combined with calcium and magnesium bicarbonate precipitation using lime. a settling zone from which the crystals that have been formed are removed and partially returned to the 1 st zone.Ī coagulant and/or flocculent will be required in order to improve the sedimentation rate and to allow the use of a rapid lamellar type settler (Densadeg type with rates of > 30 m.a zone where recirculated crystals, water to be treated and lime are thoroughly combined.Therefore, the reactor and separator used will have to be bigger, see chapter flocculators – settling tanks – flotation units.Ī good carbonate removal unit must, therefore, include: In particular, when Mg(OH) 2 is precipitated, it will tend to slow precipitation down and above all to significantly lighten the crystal aggregates that have formed. This applies at least when the surface of the available crystals remains sufficiently "clean": no impurities such as adsorbed organic polymers, colloids, metal hydroxides. conversely, in the presence of crystals, precipitation takes place very fast and a balance is achieved within a few minutes.We will then observe a gradual but often quick scaling take place in the absence of crystallisation seeds, precipitation will be very slow, water will remain supersaturated and precipitation of the few suspended substances will tend to take place but mainly over available surfaces, especially if they are metal surfaces (reactor walls, agitators, channels, valves…).The calcium carbonate formed will be crystalline and, accordingly, have precipitation kinetics that obey the germination-crystallisation laws, viz: Changes in water titres based on the amount of lime injected crystallisation mechanism theoretical bases for gas/liquid exchangesĬlick here to create your account in order to view the illustrations Figure 5.reagent and treatments than can be used.fundamental concepts on the oxidation-reduction chemical reaction.purpose of oxidation-reduction treatments.operation and maintenance of a total demineralisation unit.demineralisation line calculation principle.filtration throught a mechanical support.removing hardness (calcium and magnesium).industrial processes and effluent treatmentįundamental physical-chemical engineering processes applicable to water treatment.treatment and conditioning of industrial water.Place the teaspoon of precipitate into its labeled cup. Scoop up the precipitate into a teaspoon until it is as full as possible. Label 3 cups sodium bicarbonate, calcium chloride, and precipitate Use a spoon or popsicle stick to scrape the precipitate into a pile. degasification, odour control, evaporation Calcium chloride Baking soda Water Procedure.flocculators – settling tanks – flotation units.fundamental biological engineering processes applicable to water treatment.fundamental physical-chemical engineering processes applicable to water treatment.
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