Stability of sodium polyphosphate dispersants in mineral processing applications

Polyphosphates are commonly used industrially to provide electrostatic stabilisation to mineral and material suspensions. Polyphosphate solutions however have shown instability under processing conditions such as high temperature and acidic pH which may lead to a reduction in dispersion properties when added to mineral or material suspensions.In this study the influence of pH, temperature and divalent cation concentration pre-treatment on polyphosphate dispersion properties is reported. Dispersion properties are determined using rheological suspension analysis. The suspensions investigated are material-based model systems of titania pigment and high purity boehmite. Infrared spectroscopy studies of polyphosphate solutions were undertaken to directly investigate the polyphosphate structure after pre-treatment. The rheological measurements show reduced polyphosphate dispersion properties with reduced pH, increased temperature and at high calcium concentrations which correlate with directly measured and reported changes in the polyphosphate structure. When pH, temperature and high divalent cation concentrations are combined, the synergistic effect on reduced polyphosphate dispersion performance is particularly prominent.

Suspension yield stress as a function of pre-treated polyphosphate solution concentration and pre-treatment: (■) no pre-treatment (fresh solution prepared at neutral pH and room temperature); and (□) pre-treated for 24 h at pH 3.5 and 90 °C. Suspension comprised 50 wt.% titania pigment at pH 9.0.Figure optionsDownload as PowerPoint slideHighlights
► The pre-treatment conditions influences the polyphosphate dispersion efficiency.
► The physical and chemical parameters have a synergistic and detrimental effect on the polyphosphate dispersion properties.
► Control of pH, temperature and cation concentrations is critical for effective dispersion properties of polyphosphate.