The concentration of the KCl solution whose conductivity is that of standard seawater (35 ‰) at 15°C

The concentration of the potassium chloride solution (KCI) which has the same conductivity as15degC at P79 standard seawater corrected to35.0000permilhas been evaluated. The variation of the conductivity ratio of KCI solutions to standard seawater (35permil) has been measured between 14.8 and15.2degC for KCI solutions whose concentration varies from 32 to 33 g.kg^-1.     

The effect of concentration and temperature on the conductivity ratio of potassium chloride solutions to standard seawater of salinity 35 ‰(Cl 19.3740 ‰)

The ratiosZ_{K,t}of electrical conductivities of potassium chloride (KCI) solutions of known concentration (K) to standard seawater at the same temperature have been measured at15degC and24degC for solutions withZ_{k,15}between 0.96 and 1.04. The "normal" concentration (N or K_{N}) givingZ_{N,15}= 1was found to beK_{N} = 32.4356gKCI/kg solution. The effect of temperature onZ_{N,t}was measured over the range15degC to30degC. Equations are given for KCI concentration as a function ofZ_{15}and the inverse function, forZ_{15}/Z_{24}as a function ofZ_{24}(to allow use of a laboratory salinometer for the KCI-seawater comparisons), andZ_{N,t}as a function of temperature.     

Ion association of chloride and sulphate with sodium,potassium, magnesium and calcium in seawater at 25°C

Stoichiometric association constants, which have been measured for the ion pairs of Cl^? and SO₄^?2 with Na⁺, K⁺, Mg²⁺, and Ca²⁺, were used to determine the speciation in an artificial sea water containing only these ions. The resulting distribution is quite different to that found in earlier models in which chloride ion association was ignored. The concentrations of chloride ion pairs with the cations are 4 to 5 times larger than the concentrations of the sulphate ion pairs with the same cations. The total activity coefficients of the neutral salts in sea water calculated from the model are in good agreement with the experimentally measured values. The concentration of MgSO₄⁰ calculated to be present agrees with the amount determined from ultrasonic absorption data. The calculated solubility of gypsum is also in good agreement with the measured values.     

Mineralogical characteristics of polymetallic sulfides from the Deyin-1 hydrothermal field near 15°S,southern Mid-Atlantic Ridge

A seafloor hydrothermal field, named Deyin-1 later, near 15°S southern Mid-Atlantic Ridge(SMAR) was newly found during the 22 nd cruise carried out by the China Ocean Mineral Resources Research Development Association(COMRA). Sulfide samples were collected at three stations from the hydrothermal field during the26 th cruise in 2012. In this paper, mineralogical characteristics of the sulfides were analyzed with optical microscope, X-ray diffractometer, scanning electron microscope and electron microprobe to study the crystallization sequence of minerals and the process of hydrothermal mineralization. According to the difference of the ore-forming metal elements, the sulfide samples can be divided into three types:(1) the Ferich sulfide, which contains mainly pyrite and chalcopyrite;(2) the Fe-Cu-rich sulfide consisting predominantly of pyrite, chalcopyrite and isocubanite, with lesser amount of sphalerite, marmatite and pyrrhotine; and(3) the Fe-Zn-rich sulfide dominated by pyrite, sphalerite and marmatite, with variable amounts of chalcopyrite, isocubanite, pyrrhotine, marcasite, galena and gratonite. Mineral precipitations in these sulfides are in the sequence of chalcopyrite(isocubanite and possible coarse pyrite), fine pyrite,sphalerite(marmatite), galena, gratonite and then the minerals out of the dissolution. Two morphologically distinct generations(Py-I and Py-II) of pyrite are identified in each of the samples; inclusions of marmatite tend to exist in the coarse pyrite crystals(Py-I). Sphalerite in the Fe-Zn-rich sulfide is characterized by a"chalcopyrite disease" phenomenon. Mineral paragenetic relationships and a wide range of chemical compositions suggest that the environment of hydrothermal mineralization was largely changing. By comparison, the Fe-rich sulfide was formed in a relatively stable environment with a high temperature, but the conditions for the formation of the Fe-Cu-rich sulfide were variable. The Fe-Zn-rich sulfide was precipitated during the hydrothermal venting at relatively low temperature.     

Equilibrium and structural studies of silicon(IV) and aluminium(III) in aqueous solution. II. Formation constants for the monosilicate ions SiO(OH)3 and SiO2(OH)2. A precision study at 25°C in a simplified seawater medium

The hydrolysis of silicic acid, Si(OH)₄, was studied in a simplified seawater medium (0.6 M Na(Cl)) at 25°C. The measurements were performed as potentiometric titrations (hydrogen electrode) in which OH⁻ was generated coulometrically. The total concentration of Si(OH)₄, B, and log[H⁺] were varied within the limits 0.00075 B 0.008 M and 2.5 -log[H⁺] 11.7, respectively. Within these ranges the formation of SiO(OH)₃⁻ and SiO₂(OH)₂²⁻ with formation constants log β₋₁₁(Si(OH)₄ SiO(OH)₃⁻ + H⁺) = −9.472 ±0.002 and log β₋₂₁(Si(OH)₄ SiO₂(OH)₂²⁻ + 2H⁺) = −22.07 ± 0.01 was established. With B > 0.003 M polysilicate complexes are formed, however, with -log[H⁺] 10.7 their formation does not significantly affect the evaluated formation constants. Data were analyzed with the least squares computer program LETAGROPVRID.