Conversion of phosphogypsum to potassium sulfate

Summary Solubility of calcium sulfate in concentrated aqueous chloride solutions is of particular significance in chloride hydrometallurgy and various crystallization processes, such as the production of potassium sulfate from phosphogypsum and potassium chloride. This paper examines an example of the second type of application in which gypsum and potassium chloride are reacted to form K₂SO₄. The solubility of phosphogypsum in aqueous solutions of KCl, HCl, and mixtures of both has first been measured at various temperatures and concentrations. The parameters investigated are HCl concentration up to 6M, KCl concentration up to 180 g L^-1 and temperature from 25 to 80°C. In addition, the influence of co-existing chloride salts, such as (HCl+KCl), on the solubility of calcium sulfate is estimated from 25 to 80°C. The solubility increases obviously with the temperature increment as it does initially with acid concentration, reaching a maximum of about 3M HCl, 130 g L^-1 KCl and then drops. At the same time, the solubility of CaSO₄·2H₂O decreases with increasing KCl concentration.     

Diagramme Polythermique Du Systeme Ternaire KCl–FeCl2–H2O Entre 0 Et 70°C

Polytherm diagram of the ternary system KCl–FeCl₂ –H₂ O between 0 and 70°C. Phase equilibria in the KCl–FeCl₂ –H₂ O system were studied over the temperature range 0–70°C by conductimetric and analytical methods. A solubility polytherm of the system was constructed. We have observed the crystallization fields of the KCl and FeCl₂ 6H₂ O (at 0°C), KCl and FeCl₂ 4H₂ O (at 15, 30 and 40°C) and KCl, FeCl₂ 4H₂ O and of a double salt KClFeCl₂ 2H₂ O are obtained at 70°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Diagramme Polythermique du Systeme Ternaire NaCl-FeCl2-H2O entre 0 et 70°C

The phase diagram of ternary system Na⁺ , Fe²⁺ /Cl⁻ -H₂ O was established over the temperature range 0–70°C by conductimetric and analytical methods. A solubility polytherm of the system was constructed. For each temperature, we have determined the nature of the solid phase in equilibrium with the solution and the limit of its area of existence. This revised version was published online in July 2006 with corrections to the Cover Date.     

Etude du Diagramme Polythermique du Système Ternaire NaCl–FeCl3–H2O de 5 à 50°C

The phase diagram of the ternary system NaCl-FeCl₃ -H₂ O was determined at four different temperatures (5, 15, 30 and 50°C) by conductometry and thermal method. The experimental results show that in the temperature range 5 to 30°C, only NaCl and FeCl₃ ×6H₂ O were present as solid phases. For the 50°C isotherm, we have observed the crystallization fields of the NaCl and FeCl₃ ×2,5H₂ O. This revised version was published online in July 2006 with corrections to the Cover Date.     

Evolution des rejets saumatres des stations de dessalement de l'eau de mer au cours de leur evaporation isotherme

Desalination of sea-water was investigated. Effluent of desalination plant was evaporated in isotherm and isobar condition. Density, electric conductivity measurements and chemical analysis were carried out during the process. The results characterising the crystalline phase provide the fields and limits of the precipitation and separation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Calcul Des Diagrammes De Phases Des Systemes Binaires H2O–MCln (M=Mg2+, Fe2+, Fe3+)

A semi-empirical model consistent with thermodynamical conditions of equilibrium was used and oriented to the calculation of phase diagrams of the binary systems H₂ O-MgCl₂ , H₂ O-FeCl₂ and H₂ O-FeCl₃ . For each solid phase, the exploitation of the experimental and bibliographical data gives a liquidus curve equation comprising a limited number of parameters. A such equation allows to calculate with precision the solubility of the stoichiometric solid phase in a large range of temperature and composition. This revised version was published online in July 2006 with corrections to the Cover Date.