Comparing iron phosphate and hematite precipitation processes for iron removal from chloride leach solutions

• Phosphate process (pH 1, 40 °C) gives 98.8% Fe removal with 2.8% Cu and 0.5% Ni loss.
• Increasing pH or temperature yields higher Ni and Cu losses with phosphate process.
• Hematite process (pH 1, 80 °C) yields 99.6% Fe removal with 1.7% Cu and 3.5% Ni loss.
• Phosphate precipitate exhibits better filterability and settling than hematite.
• Iron phosphate precipitation can be a suitable alternative iron removal process.

The presence of iron in pregnant leach solutions presents significant processing challenges. The removal of iron impurities from leach solutions by means of iron phosphate precipitation may be a feasible alternative to more conventional iron oxide/iron hydroxide precipitation processes. This study compares the performance of the iron phosphate precipitation process with that of the hematite process at different operating temperatures (40 °C–90 °C), pH conditions (pH 1–pH 3) and seeding measures for the removal of iron from a chloride leach solution. The extent of iron removal, co-precipitation of nickel and copper, and solid-liquid separation were used as performance criteria for the comparison.Seeded iron phosphate precipitation at pH 1 and 40 °C resulted in 98.8% iron removal with 0.5% nickel and 2.8% copper losses. 99.8% iron removal was achieved with the iron phosphate precipitation process at pH 1 and 80 °C, but the nickel and copper losses increased to 8.7% and 20.8%, respectively, with the increase in temperature. Seeded hematite precipitation at pH 1 and 80 °C yielded 99.6% iron removal with 3.5% nickel and 1.7% copper losses. For the hematite process, nickel and copper losses decreased with an increase in temperature. Increasing the pH yielded higher nickel and copper losses for both processes.All seeded precipitation experiments produced easily filterable precipitates. Unseeded iron phosphate precipitates produced at 40 °C and pH 1 were filterable, but increased nickel and copper losses were observed. Unseeded hematite precipitation resulted in high nickel and copper losses, with the precipitates practically impossible to filter. Iron phosphate precipitates exhibited more favourable settling characteristics than the precipitate produced with the hematite process.