Calcite concentrations

Calcite-dolomite collectors Recovery (%) Nb205 depressant used during CaO flotation % Nb205 in calcite concentrate Flotation pH... 

Emulsified fatty acid with soda ash and silicate was used in the calcite circuit. Xanthate was added to the emulsion, where pyrite was floated with the calcite/ dolomite concentrate. Using this calcite/dolomite system, the calcite/ dolomite recovery to the calcite concentrate increased from 55% to 80%, respectively. 

Fig. 2. The interaction of the ranges of influence for several calcite cement nuclei. Note that nucleation of calcite cement may possibly take place at a dissolved calcite concentration significantly lower than the solubility of biogenic carbonate.

The calcium concentrations used in some of the experiments were close to (and sometimes beyond) solubility limits. To determine the solubility of calcium in the systems used, calculations were carried out, first for calcium concentrations between 0.5 and 5 mM, and, second, pH values of 2 to 12 for all calcium concentrations. The solubility of calcium is obviously higher at low pH up to pH 8, where precipitation occurs at a concentration of 3 mM CaCh. Figure A5.4 shows the calcite concentration as a function of calcium concentration at pH 8 where the transition between the soluble form and the precipitate occurs. 

Figure A5.4 Calcium solubility (at pH 8). Calcite concentrations are 0.17 mM at 3 mM calcium and 2.17 mM at 5 mM calcium.

The effect of DOM on calcium solubility is less apparent than expected. Calcite precipitates, as in the absence of DOM (Figure AS.4), from a calcium concentration of 3 mM, as shown in Figure A5.8. However, the calcite concentration is now varied with a concentration of 0,12 at 3 mM and 2,12 at 5 mM. The calcite concentration is reduced by the concentration of the Ca-DOM complex (see Figure A5.9). 

Figure 7.6 shows the pH (on the left side) and the temperature (on the right side) for the flow inside the cavity. A vortex appears in the center of the cavity due to variations of temperature and calcite concentration. The fluid moves slowly in a free convection cell. The results for the pH and temperature compare favorably with the ones from Genthon et al. [9]. While the pH (and PCO2) decreases with the depth, the temperature increases from 1 (300 K) to 1.4 (420 k). The deflections of the lines are due to the temperature and concentration gradients. The solubility of calcite is a function of the pH of the fluid, as well as of the calcium, Ca, concentration and ions of carbonate concentration. 

Stability. AH calcitic and dolomitic limestones are extremely stable compounds, decomposing only in fairly concentrated strong acids or at calcining temperatures of 898°C for high calcium and about 725°C for dolomitic stones at 101.3 kPa (1 atm). A very mild destabilizing effect is caused by C02-saturated water, as described in the preceding section on solubihty. Aragonite, however, is not as stable as calcite. In sustained contact with moisture,... 

A U.S. Bureau of Mines survey covering 202 froth flotation plants in the United States showed that 198 million tons of material were treated by flotation in 1960 to recover 20 million tons of concentrates which contained approximately 1 billion in recoverable products. Most of the worlds copper, lead, zinc, molybdenum, and nickel are produced from ores that are concentrated first by flotation. In addition, flotation is commonly used for the recoveiy of fine coal and for the concentration of a wide range of mineral commodities including fluorspar, barite, glass sand, iron oxide, pyrite, manganese ore, clay, feldspar, mica, sponumene, bastnaesite, calcite, garnet, kyanite, and talc. 

Some reduction in surface tension is also claimed (due to the formation of calcite and a consequential reduction in the ionic concentration of the water), although this is unlikely to provide any practical benefit. 

Carbonate in boilers usually is present as a hard, dense, white to tan or brown calcite scale (CaC03). A tan to brown color usually indicates the presence of iron. Samples of scales and deposits normally fizz when tested with concentrated muriatic acid (hydrochloric acid, HC1) if carbonate is present, although some preliminary heating may be required. 

Fig. 2.8. Relation between the Ca and CR concentrations of geothermal waters and inclusion fluids. Solid lines indicate (1) albite-K-feldspar-muscovite-quartz-caleite-solution equilibrium at OHaCOs = 10 (2) albite-K-feldspar-muscovite-quartz-calcite-solution equilibriumn at oh2C03 = 10 (3) anhydrite-solution at SSo (total dissolved sulfate concentration) = 10 and (4) anhydrite-solution equilibrium at SSq = 10. For symbols used see caption to Fig. 2.2 (Shikazono, 1978a).

If calcite is in equilibrium with the aqueous solution, the relationship between pH and the concentration of Ca " " can be obtained from reaction (2-10). 

This equation shows that activity of Ca + is related to pH, concentration of H2CO3 and temperature. Because pH is related to the concentration of Cl for the equilibrium curves 1 and 2 in Fig. 2.14, the relationship between the concentrations of Ca " " and Cl" can be derived for calcite-albite-sericite-K-feldspar-quartz equilibrium (curves 4 and 7 in Fig. 2.14) and calcite-albite-sericite-Na-montmorillonite-quartz equilibrium (curves 5 and 8 in Fig. 2.14) with constant w2h2C03- The range of zh2C03 in the solution in equilibrium with calcite is assumed to be 10 to 10 . The other equilibrium curves for the assemblage including Ca minerals are also drawn (Fig. 2.14). These assemblages are wairakite-albite-sericite-K-feldspar-quartz (curve 3), Ca-montmotillonite-albite-sericite-Na-montmorillonite-quartz (curve 6), Ca-montmorillonite-albite-sericite-K-feldspar-quartz (curve 9) and anhydrite (curve 10). The effect of solid solution on the equilibrium curves is not considered because of the lack of thermochemical data of solid solution. 

Fig. 2.14. The variation of concentration of with concentration of CP in aqueous solution in equilibrium with a given mineral assemblage at 250°C. I Equilibrium curve based on albite-sericite-Na-montmorillonite-quartz-aqueous solution equilibrium and Na-K-Ca relationship obtained by Fournier and Truesdell (1973). 2 Equilibrium curve based on albite-K-feldspar-aqueous solution equilibrium and Na-K-Ca relationship obtained by Fournier and Truesdell (1973). 3 Wairakite-albite-sericite-K-feldspar-quartz. 4 Calcite-albite-sericite-K-feldspar-quartz (/jjhjCO, = 10 ). 5 Calcite-albite-sericite-Na-montmorillonite-quartz (mH2C03 = 10 ). 6 Ca-montmorillonite-albite-sericite-Na-montmorillonite-quartz. 7 Calcite-albite-sericite-K-feld-spar-quartz (mnjCOj = 10 ). 8 Calcite-albite-sericite-Na-montmorillonite-quartz (mHjCOj = 10 ). 9 Ca-montmorillonite-albite-sericite-K-feldspar-quartz. 10 Anhydrite = 10 ). (Shikazono, 1976)...

The Okuaizu geothermal system is characterized by high temperatures (maximum 340°C), high salinity (about 2 wt% total dissolved solids (TDS)) and large amounts of non-condensable gases (1 wt% CO2 and 200 ppm H2S). The pH of the hydrothermal solution measured at 25°C is 6.44 (Table 2.6). However, the pH of the original fluid in the reservoir is computed to be 4.05. This pH as well as alkali and alkali earth element concentrations are plotted near the equilibrium curve of albite, K-mica, anhydrite and calcite (Fig. 2.19) (Seki, 1991). 

Fig. 2.19. Reservoir temperature versus saturation indices (logQ/K) for calcite, anhydrite, K-feldspar and K-mica based on the estimated composition of reservoir fluid (Seki, 1991). Estimation based on gas results of Seki (1990), with saturation calculations carried out by PECS (Takeno, 1988). Gas concentrations were assumed to be 1 wt% of CO2 and 250 mg/kg for H2S for all wells (Seki, 1991).

The H2S concentration of hydrothermal solution is plotted in Fig. 2.33. Based on these data, we can estimate the temperature of hydrothermal solution buffered by alteration mineral assemblages such as anhydrite-pyrite-calcite-magnetite and pyrite-pyrrhotite-magnetite for Okinawa fluids. 

For example, assuming anhydrite-magnetite-calcite-pyrite-pyrrhotite buffers redox in sub-seafloor reaction zones and a pressure of 500 bars, dissolved H2Saq concentrations of 21 °N EPR fluid indicate a temperature of 370-385°C. However, the estimated temperatures are higher than those of the measurement. This difference could be explained by adiabatic ascension and probably conductive heat loss during ascension of hydrothermal solution from deeper parts where chemical compositions of hydrothermal solutions are buffered by these assemblages. 

Fig. 2.33. H2Saq concentration.s as a function of temperature for hot spring fluids at midocean ridges as a function of redox. Assuming AMPC (anhydrite-magnetite-pyrite-calcite) and PPM (pyrite-pyrrhotite) buffers redox in sub-seafloor reaction zones and a pressure of 500 bars, dissolved H2Saq concentrations indicate temperatures of approximately 370-385°C. Solid star Okinawa. (Modified after Seyfried and Ding, 1995.)...

Shikazono (1978) theoretically derived that the concentrations of alkali and alkali earth elements in chloride-rich hydrothermal solution are nearly in equilibrium with hydrothermal alteration minerals such as albite, K-feldspar, K-mica, quartz, calcite, wairakite, and Mg-chlorite. If we use 500 mmol/kg H2O as the average Cl concentration of hydrothermal solution from the back-arc basin, which is in equilibrium with... 

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