Isothermes 75 °C, des systèmes ternaires limitant le système quaternaire réciproque: H+, K+, PO43−, SO42−, H2O

Abstract

The five ternary isotherms limiting the quaternary system mentioned in the title have been established as a first step toward the study of this system at 75 °C and 1 atm (101.3 kPa). This temperature has been chosen in order to be able to apply the results to the industrial preparation of phosphopotassium fertilizers through a sulphuric treatment of a phosphate ore for which the optimum temperature is 70–80 °C. (i) Anhydrous reciprocal ternary system: H2SO4–H3PO4–K2SO4–K3PO4. Solid phases: KHSO4, KH2PO4•KHSO4, KH5(PO4)2, and a solid substituting solution K8(H2PO4)1+x(HSO4)7−x, 0 ≤ x ≤ 1, continuous between the two limiting compositions KH2PO4•7KHSO4 and KH2PO4•3KHSO4 for which the indexed powder diagrams are given. (ii) Ternary system K3PO4–H3PO4–H2O. Solid phases: KH5(PO4)2, KH2PO4, 3K2HPO4•KH2PO4•2H2O, K2HPO4, and K3PO4•3H2O. (iii) Ternary system K2SO4–H2SO4–H2O. Solid phases: K2SO4, K2SO4•KHSO4, K2SO4•7KHSO4•H2O, and KHSO4. A phenomenon of retrosolubility as a function of the water content has been observed. (iv) Ternary system K2SO4–K3PO4–H2O. Solid phases: K2SO4 and K3PO4•3H2O. (v) The ternary system H3PO4–H2SO4–H2O is formed by only one liquid phase at 75 °C. [Journal translation]