Salinity, solubility dependence

Solubilities of quartz and amorphous silica in aqueous solutions increase with increasing of temperature (Holland and Malinin, 1979). Solubility of barite depends on salinity and temperature (Blount, 1977). The solubility of barite in hydrothermal solution having more than 1 molal NaCl concentration increases with increasing temperature, while a solubility maximum exists in the solution with NaCl concentration less than ca. 0.2 molal (Blount, 1977). 

The solubilities of ore metals depend on several variables such as /sj, /02 pH, salinity, SS and temperature (Barnes and Czamanske, 1967 Shikazono, 1972b Barnes, 1979). 

According to these previous studies, the most dominant dissolved states of Au and Ag in ore fluids are considered to be bisulfide and chloride complexes, depending on the chemistry of ore fluid (salinity, pH, redox state, etc.). However, very few experimental studies of Au solubility due to chloride complex and Ag solubility due to bisulfide complexes under hydrothermal conditions of interest here have been conducted. Thus, it is difficult to evaluate the effects of these important species on the Ag/Au of native gold and electrum. Other Au and Ag complexes with tellurium, selenium, bismuth, antimony, and arsenic may be stable in ore fluids but are not taken into account here due to the lack of thermochemical data. 

Let us illustrate this phenomenon with a practical example, the variation of oxygen and of nitrogen equilibrium solubilities with depth in the ocean [1]. For seawater, the density p depends on temperature and salinity, and it could vary from 1.025 to 1.035 g cm. For dissolved oxygen, V2 = 0.97 cm g in seawater at a water temperarnre near 25°C. If d is expressed in meters, then at the lower limit of the water density. Equation (21.17) becomes... 

Bunsen solubility coefficient (a ) The term that relates the concentration of a gas in seawater to its partial pressure in the atmosphere. It is dependent on temperature and salinity. 

The degree to which a water sample will be anomalous with respect to proximal or distal mineralization depends on the solubility of the species that reflect that style of mineralization under the prevailing pH, Eh, and salinity conditions. Ideally, the geochemical explorationist would like any sample medium to have anomalies in all species that define the style of mineralization. In reality, this is rarely, if ever, the case. However, although waters and sediments will not necessarily have anomalies in all the relevant elements, it is important to understand why this is the case and avoid the temptation to include elements that are not diagnostic of the style of mineralization. 

This relationship varies slightly because of the vertical fluctuation in the phosphorus content in the sea. For saline water systems, data on the solubility product of a calcium phosphate is difficult to obtain inasmuch as — aside from temperature and hydrostatic pressure — the solubility product is dependent on the type and amount of solutes present. The apparent dissociation constants of H3P04 are defined by the equations129,130 ... 

Dissolved oxygen levels in water depend, in part, on the chemical, physical and biochemical activities occurring in the water. Oxygen has a limited solubility in water directly related to atmospheric pressure and inversely related to water temperature and salinity. Low-dissolved oxygen levels can limit the bacterial metabolism of certain organic compounds. 

The existence and direction of a CO2 flux between the atmosphere and the ocean can be determined by the difference in partial pressure of CO2 ipco) in seawater and in the overlying atmosphere, pco in seawater depends on its solubility and the concentration of dissolved CO2 (with solubility inversely related to temperature and salinity). CO2 gas diffusing into water... 

Air-saturated water has a dissolved O2 concentration dependent on temperature, the Henry s law constant and ionic strength. In pure water at 0 °C, O2 saturation is 450 p,M at 25 °C, saturation falls to 270 p,M. Other solutes reduce O2 solubility, such that at normal seawater salinities, O2 saturation is reduced by —25%. Seawater is, of course, rarely at perfect O2 saturation. Active photosynthesis may locally increase O2 production rates, resulting in supersaturation of O2 and degassing to the atmosphere. Alternately, aerobic respiration below the sea surface can consume dissolved O2 and lead to severe 02-depletion or even anoxia. 

Sodium bicarbonate Sodium bicarbonate (NaHCOs) is an odorless, white crystalline powder with a saline, slightly alkaline taste. A variety of particle-size grades of powders and granules are available. The carbon dioxide yield is approximately 52% by weight. At RH below approximately 80% (at room temperature), the moisture content is less than 1%. Above 85% RH, it rapidly absorbs an excessive amount of water and may start to decompose. Its solubility in water is 1 part in 11 parts at 20°C, and it is practically insoluble in 95% ethanol at 20°C. When heated to 250-300°C, NaHCOs decomposes and is converted into anhydrous sodium carbonate. However, thisprocess is both time-and temperature-dependent, commencing at about 50°C. The reaction proceeds via surface-controlled kinetics, and when NaHCOs crystals are heated for a short period of time, very fine needle-shaped crystals of anhydrous sodium carbonate appear on the surface. ... 

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