Calcium carbonate metal adsorption

After an extensive study of the adsorption of arsenious oxide by metallic hydroxides,3 Sen concluded that this type of adsorption resembles that of cations by manganese dioxide, and that the chemical affinity between the adsorbent and the substance adsorbed plays an important part, thus differing from adsorption by charcoal. It has been observed that soils having a high absorption capacity for bases also absorb the arsenite ion from solutions of 0-001 to 0-01X concentration.4 The absorption increases with time, without reaching an end-point, and the process follows the normal adsorption equation C1=kC1Jn. The addition of ferric oxide or calcium carbonate to the soil considerably increases the capacity for absorption, but such salts as calcium sulphate or copper sulphate have no effect. 

Adsorption This method is the simplest way to immobilize enzymes. Enzymes can be adsorbed physically on a surface-active adsorbent by contacting an aqueous solution of enzyme with an adsorbent. Commonly employed adsorbents are (Zaborsky, 1973) alumina, amon-exchange resins, calcium carbonate, carbon, cation-exchange resins, celluloses, clays, collagen, colloid-ion, conditioned metal, glass plates, diatomaceous earth, and hydroxyapatite. The advantages of adsorption techniques are as follows ... 

A number of adsorption studies have been conducted for the adsorption of transition and heavy metals on carbonates. Mn2+ adsorption has been the most intensely studied mechanism. This is possibly because of its importance to carbonate mineral behavior in marine sediments (see Chapter 4). Studies of Mn2+ interaction with the surface of calcite in dilute aqueous solutions indicated that Mn2+ uptake is approximately balanced by Ca2+ release (McBride, 1979). It was suggested that the calcium release may not be the result of direct displacement, but rather results from the following reactions ... 

Generally, the concentrations of the interfering transition metal ions in the brine are decreased sufficiently by simple adsorption onto the colloidal precipitates of calcium carbonate, magnesium carbonate, and barium sulfate produced by conventional brine pretreatment. The brine is then acidified with hydrochloric acid to about pH 4. This helps to maintain a high hydrogen overvoltage on mercury in order to minimize the formation of hydrogen in the... 

Stabilization. For example, calcium stearate may play the role of an associate thermal stabilizer when used in a system with calcium salts of fatty acids. These stabilizers use combinations of two or more metals - one of which (e.g. zinc) produces metal chlorides which accelerate PVC degradation. The presence of large amount of calcium salts helps to convert this chloride to calcium chloride which does not increase the degradation rate of PVC. Also, calcium carbonate can react with hydrogen chloride which is produced as PVC degrades. On the other hand, inclusion of fillers which contain admixtures of metals such as iron, nickel, copper, etc. reduces PVC thermal stability. Fillers also affect UV stabilization by adsorption of HALS stabilizers which immobilizes them and prevents them from performing as radical scavengers. 

Zachara, J. M., C. E. Cowan, and C. T. Resch. 1993. Metal cation/anion adsorption on calcium carbonate Implications to metal ion concentrations in ground water. In Met-... 

Zachara JM, Kittrick JA, Harsh JB (1988) Geochim Cosmochim Acta 52 2281 Zachara JM, Cowan CE, Resch CT (1993) Metal cation/anion adsorption on calcium carbonate. In AUen HE, Perdue EM, Brown DS (eds) Metals in groundwater. Lewis Publishers, Boca Raton, p 37... 

Calcium phosphate and metal carbonates are relatively insoluble salts that could form adsorption layers or solid solutions at a calcite surface. 

The first reaction predominates if the product contains a large amount of water (-18%). This reaction is analogous to the disproportionation of aqueous hypochlorite. However, disproportionation is much slower in solid calcium hypochlorite than in solution. Under dry conditions, the second reaction predominates. It is catalyzed by transition metals including iron and manganese. It may occur explosively 150°C. Thus, calcium hypochlorite products usually contain some water or an additive such as magnesium sulfate heptahydrate. The third reaction is the reverse of chlorination. The fourth reaction is due to the adsorption of carbon dioxide from air or the release of carbon dioxide from carbonate salt impurities. It is accelerated by water and temperature. The first reaction accounts for -70%, and the second reaction -30%, of the decomposition of solid calcium hypochlorite made in the United States and stored in sealed containers at 25°C. ... 

Examples The roasting of ores, the chemical adsorption of hydrogen sulfide by metal oxides (forming sulfides), the conversion of a metal oxide with a volatile non-metal oxide into a salt (e.g., the chemical adsorption of sulfur dioxide and oxygen by calcium oxide), the reductive chlorination of ilmenite (iron titanate) whereby iron chloride and titanium oxide are formed. In some processes a second solid reactant is present (e.g., carbon) that also reacts with the gaseous reactant, forming another gaseous reactant (e.g., carbon monoxide). 

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