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. You can see a white precipitate is deposited at the bottom of the solution when two solutions are mixed. purpose of oxidation-reduction treatments Calcium chloride (CaCl 2) reacts with aqueous NaOH to produce calcium hydroxide ( Ca (OH) 2 ) and NaCl. 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. degasification, odour control, evaporation. 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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