Precipitation Inhibitor Research Articles

Effect of precipitation inhibitors on calcium carbonate scale formation

Threshold levels of chemical inhibitors are often used to kinetically prevent scale from forming. No theory exists which predicts the minimum level of scale inhibitor concentration which may be effective under varying aqueous solution conditions. When ionic calcium concentration is much greater than ionic carbonate, a model is proposed based upon the relative diffusion rates of the carbonate and the inhibitor ions from which the following criterion for the minimum concentration of inhibitor, which might be effective, is developed and tested: Z In(In z- ) > 2(CO 2- 3), where Z In is the magnitude of the charge on the inhibitor ion and () denotes molar concentration.

Observations Supporting Phosphate Removal by Biologically Mediated Chemical Precipitation – A Review

Chemical precipitation of phosphorus in biological treatment plants may be mediated biologically in at least two ways. First the elevated P-concentrations created by anaerobic phosphate release from bacteria can initiate and accelerate calcium phosphate precipitation. Secondly biological denitrification in fixed biofilms and possibly also in bacterial floes can lead to phosphate precipitation due to the elevated pH-conditions inside the biofilms. In both cases the bulk precipitation conditions must be generally favourable, i.e. the calcium concentration should be reasonably high, roughly above 50 mg/ℓ, and the concentration of precipitation inhibitors low: magnesium, pyrophosphates and bicarbonate (alkalinity). With respect to accelerated bulk precipitation it is also essential that the pH is relatively high, preferably above 7.5. Biologically mediated phosphate precipitation is only two P-removal mechanisms out of several mechanisms. Apart from normal biological P-assimilation phosphate can be removed through polyphosphate accumulation in bacteria and through normal chemical bulk precipitation. The paper gives a survey of the mechanisms. Virtually all the published literature on P-removal in biological treatment plants contain insufficient data to evaluate the alternative P-removal mechanisms. In particular there is a need for agreement on procedures with which to characterize the P-fractions in the sludge in order to determine how much P is removed by the bacteria and by mineral phases. Still much qualitative and quantitative knowledge is required on both the biological and chemical P-removal mechanisms before reasonable optimization strategies and design criteria can be outlined.

Aboral depressions in the tests of the sea urchin Tripneustes cf. gratilla (L.) in the Gulf of Eilat, Red Sea

Flattening and aboral depressions occurred in high proportions in Tripneustes cf. gratilla (L.) populations that inhabited an artificial lagoon in the northern Gulf of Eilat, Red Sea. The average test height to diameter ( H D ) ratio of the most affected population, near a small wastewater outlet, was 0.43 ± 0.01 (Se) and 76% showed aboral depressions. The H D ratio was 0.54 ± 0.01 in populations outside the lagoon and <1% exhibited aboral depressions. The exposure of normal T. cf. gratilla to industrial CaCO 3 precipitation inhibitors affected the growth and H D ratio in a similar manner within 30–45 days. The light-weight tests of the deformed urchins and the occurrence of skeletal resorption in the interior part of the test indicate that the unknown pollutant, possibly contained in laundry wastewater, reduced calcification by these animals and resulted in a mechanical collapse of the tests. A regular pattern of small pits at the aboral tip of the ambulacra suggests that intestinal mesenterial threads, attached to the test at the same points from within, facilitated this collapse by a mechanical pull. The normal test morphology of the regular echinoids may be regulated by the mechanical activity of various contractile and elastic tissue elements, among which mesenterial threads are probably included.

Ionic Activity Products and Crystal Forms of Calcium and Magnesium Carbonates Precipitated from Calcium‐Magnesium Bentonites

AbstractA series of laboratory experiments were conducted to study quantities, mineral forms, and solubility of alkaline earth carbonates precipitated from Ca‐Mg‐bentonite systems. The effects of Mg on carbonate precipitation and solubility were assessed in isolation from other carbonate precipitation inhibitors commonly found in soils. Five bentonite systems were preconditioned by saturation with different proportions of exchangeable Ca and Mg. Calcium/magnesium ratios ranged from 99:1 to 8:92. Portions of each system were seeded with calcite, and both seeded and unseeded systems were equilibrated with deionized water or NaHCO3. Equilibrium solution concentrations of Ca, Mg, Na, HCO3, and Cl and also pH served as input data to the WATEQF solution chemistry computer program for calculations of ion strength, ion pairs, ion activities, and carbonate ionic activity products (IAP).The data obtained from the series of experiments clearly demonstrated that solubility characteristics of calcium carbonate in the Ca‐Mg‐bentonite systems were influenced by incongruent properties of freshly precipitated carbonate surfaces. The data further show that Mg inhibited crystallization and increased solubility of calcium carbonate and that high concentrations of Mg in the NaHCO3‐bentonite precipitation medium induced crystallization of Mg calcite. In some systems, Mg was precipitated in forms which were not identified by either x‐ray diffraction analysis or IAP characteristics.