Calcium leaching

Fig. 2. Calcium leached during sequential batch extractions of solidified/stabilized hazardous wastes...

Figure 3. Calcium leaching rates of Micrite, Marble, and Salem Limestone at pH=3.0.

Figure 5.20. Movement of Ca in the form of CaCOj, CaCb, and CaS04 by water leaching through an oxisol. The Ca was initially added to the soil surface. (Adapted from K. D. Ritchey et al. 1980. Calcium leaching to increase rooting depth in a Brazilian savannah oxisol. Agron. I. 72 40-44.)...

Contact between water and cement materials can lead to lime (calcium) leaching, which induces a substantial pH increase in the drinking water. The effect on water quality can be seen as ... 

Portland cements of various phase composition do not give special differences in amount of calcium leached, while the slag cements do [98], At paste surface car-bonation the leaching of calcium is greatly reduced. This process results in gradual... 

Y. Furusawa, Research trends on degradation of concrete caused by calcium leaching and modeling. Concrete J. (JCI), 35(12) (1997) 29 (in Japanese). 

Comparison between samples made with the blended binder and with OPC indicated that the level of sulphur (as sulphate) and calcium leached from the samples made with the novel binders under high pressure water was more than from those made using OPC. This could be due to the lower hydration rate and reduced cementitious matrix available to bind the sulphates and calcium ions formed in samples made with novel cement. However, the conditions under which the high pressure through-flow test is carried out ai e much more accelerated than normal ground conditions. Thus, dissolution of a high level of sulphate ions is not expected using these novel binders. 

Historically, soda ash was produced by extracting the ashes of certain plants, such as Spanish barilla, and evaporating the resultant Hquor. The first large scale, commercial synthetic plant employed the LeBlanc (Nicolas LeBlanc (1742—1806)) process (5). In this process, salt (NaCl) reacts with sulfuric acid to produce sodium sulfate and hydrochloric acid. The sodium sulfate is then roasted with limestone and coal and the resulting sodium carbonate—calcium sulfide mixture (black ash) is leached with water to extract the sodium carbonate. The LeBlanc process was last used in 1916—1917 it was expensive and caused significant pollution. 

In cyanidation, the ground ore is leached with a solution of sodium cyanide (0.02—0.05%) or an equivalent of calcium cyanide together with some lime. The leaching solution is aerated to provide oxygen and gold is dissolved with formation of sodium dicyanoauratae(-l) [15280-09-8] 5 2l(J u(C2>5)[) (see... 

The rate of dissolution is limited by oxygen availabiUty rather than by cyanide concentration. When oxygen solubiUty is reduced by water salinity or by consumption by ore constituents such as sulfide minerals, enrichment of the air with oxygen or addition of hydrogen or calcium peroxide improves leaching kinetics and decreases cyanide consumption (10). 

The calcium oxide is leached out with acid (HCl), leaving a finely divided T1H2 powder. 

Opa.nte. There are two methods used at various plants in Russia for loparite concentrate processing (12). The chlorination technique is carried out using gaseous chlorine at 800°C in the presence of carbon. The volatile chlorides are then separated from the calcium—sodium—rare-earth fused chloride, and the resultant cake dissolved in water. Alternatively, sulfuric acid digestion may be carried out using 85% sulfuric acid at 150—200°C in the presence of ammonium sulfate. The ensuing product is leached with water, while the double sulfates of the rare earths remain in the residue. The titanium, tantalum, and niobium sulfates transfer into the solution. The residue is converted to rare-earth carbonate, and then dissolved into nitric acid. 

Wet Process. The sodium arsenate and stannate slag are treated by a leach and precipitation process to produce calcium arsenate, calcium stannate, and a sodium hydroxide solution for recycle. The sodium antimonate filtercake containing selenium, tellurium, and indium is treated in a special metals refinery to recover indium and tellurium. 

A number of high temperature processes for the production of titanium carbide from ores have been reported (28,29). The aim is to manufacture a titanium carbide that can subsequently be chlorinated to yield titanium tetrachloride. In one process, a titanium-bearing ore is mixed with an alkah-metal chloride and carbonaceous material and heated to 2000°C to yield, ultimately, a highly pure TiC (28). Production of titanium carbide from ores, eg, ilmenite [12168-52-4], EeTiO, and perovskite [12194-71 -7], CaTiO, has been described (30). A mixture of perovskite and carbon was heated in an arc furnace at ca 2100°C, ground, and then leached with water to decompose the calcium carbide to acetjdene. The TiC was then separated from the aqueous slurry by elutriation. Approximately 72% of the titanium was recovered as the purified product. In the case of ilmenite, it was necessary to reduce the ilmenite carbothermaHy in the presence of lime at ca 1260°C. Molten iron was separated and the remaining CaTiO was then processed as perovskite. 

Other Reductions. Ductile, pure zirconium has been made by a two-stage sodium reduction of zirconium tetrachloride (68) in which the tetrachloride and sodium are continuously fed into a stirred reactor to form zirconium dichloride [13762-26-0], heating with additional sodium yields zirconium metal. Leaching with water removes the sodium chloride from the zirconium. Bomb reduction of pure zirconium tetrafluoride with calcium also produces pure metal (69). 

Finely divided zirconium powder is made by bomb reduction of zirconium oxide with magnesium or calcium. The powder is separated by leaching... 

Decomposition with Bases. Alkaline decomposition of poUucite can be carried out by roasting poUucite with either a calcium carbonate—calcium chloride mix at 800—900°C or a sodium carbonate—sodium chloride mix at 600—800°C foUowed by a water leach of the roasted mass, to give an impure cesium chloride solution that is separated from the gangue by filtration (22). The solution can then be converted to cesium alum [7784-17-OJ, CS2SO4 Al2(S0 2 24H20. Extraction of cesium from the poUucite is almost complete. Solvent extraction of cesium carbonate from the cesium chloride solution using a phenol in kerosene has also been developed (23). 

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