Thermochemistry of the nickel–phosphorus system

In the first part, an extensive overview is given over the thermodynamic information for the nickel–phosphorus system which is available in the literature. In the second part, phosphorus vapor pressure measurements over nickel–phosphorus alloys are described for which an isopiestic method was employed. Data points were obtained between 33.82 and 44.40 at% P in the temperature interval from 977 to 1325 K. Based on these measurements partial thermodynamic properties and integral Gibbs energy values were determined. The standard molar Gibbs energy of formation of Ni₅P₄ for the temperature range 977–1042 K was obtained as:${\mathrm{\Delta }}_{\text{f}}{G}_{\text{m}}^{\text{o}}\left({\text{Ni}}_5{\text{P}}_4\right)\left(\text{s}\right)\pm 9.8/\left(\text{kJ}{\text{mol}}^{?1}\right)=?632.1+0.2136T/\text{K}$     

Leaching optimization and dissolution behavior of alkaline anions in bauxite residue

Bauxite residue is a highly alkaline waste containing soluble alkaline anions, which can cause environmental concerns. The optimal leaching conditions, distribution of alkaline anions, types of pivotal alkaline anions and their dissolution behaviors were investigated based on the combination of single factors-orthogonal experiments and leaching stage experiment. Using a two-stage leaching, 86% of the soluble alkaline anions $\left({\text{CO}}_3^{2?},{\text{HCO}}_3^{?},\text{Al}{\left(\text{OH}\right)}_4^{?},{\text{OH}}^{?}\right)$ were leached with a L/S ratio of 2 mL/g, at 30 °C, over 23 h. During the first stage of leaching, approximately 88% of alkaline anions were leached from the dissolution of free alkali (NaOH, carbonate, bicarbonate, NaAl(OH)₄) with the rest originating from the dissolution of alkaline minerals (calcite, cancrinite and hydrogarnet). Supernatant alkalinity was 69.78 mmol/L with ${\text{CO}}_3^{2?}$ accounting for 75%. Furthermore, carbonate leaching was controlled by solid film diffusion using the Stumm Model with an apparent activation energy of 10.24 kJ/mol.