PURIFICATION OF PREGNANT LEACHING SOLUTION OF HIGH PRESSURE ACID LEACHING (HPAL) NICKEL'S RESIDUES FOR SYNTHESIS OF IRON PHOSPHATE AS A RAW MATERIAL OF BATTERY CATHODE MATERIAL

• Main Author: Zaidan Al Fikri, Muhammad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/76803
• Institution: Institut Teknologi Bandung

Currently, commercial extraction of nickel from low-grade limonite ore is generally carried out through the High Pressure Acid Leaching (HPAL) process. One of the problems faced by the HPAL plant is a very large volume of residue with a tonnage of about 1.4-1.6 times that of the feed ore. HPAL plant residue is an environmental issue and its utilization has not been widely conducted. The main content of HPAL residue is iron (Fe), and one of the potential utilizations of the residue is to prepare iron phosphate (FePO4) which can be used as a raw material for cathode lithiumion batteries of the LiFePO4 type (LFP). To produce pure FePO4, the leaching solution must be purified, especially to separate Al from Fe. In this research, purification of the HPAL residue leaching solution was carried out to separate Al from Fe and produce a high purity FePO4 precursor solution. A series of experiments were carried out to synthesize FePO4 from nickel HPAL plant residue which included leaching of the residue in 5 M H2SO4 solution, Fehydroxide precipitation, Al leaching in Fe-hydroxide precipitate with NaOH solution (caustic leaching), re-leaching of the Fe-rich residue from caustic leaching with 5 M H2SO4 solution, and precipitation of iron phosphate. Leaching of iron with 5 M H2SO4 solution was carried out to dissolve Fe with conditions referring to previous studies. Hydroxide precipitation experiments were carried out under a variation of pH of 2.5 – 5.0 to separate Fe from Al. Caustic leaching of the Fe-Alhydroxide precipitate was carried out to dissolve Al which was co-precipitated with Fe under variations of NaOH concentrations of 150–300 g/L, temperature 70–100 °C, solid/liquid ratio (S/L) of 0.25–0.40 g/mL, and leaching time of 10–50 minutes. The Fe-rich residue obtained was then re-leached with 5 M sulfuric acid to redissolve the Fe and producing a precursor solution for FePO4 precipitation. FePO4 precipitation was carried out using diammonium phosphate (DAP). The results of the hydroxide precipitation experiment showed that the percentage of Fe and Al precipitation increased with increasing pH from 2.5 to 5. The highest selectivity value of Fe to Al precipitation was obtained at pH 3, which was 0.52. The caustic leaching experiment gave the highest percentage of Al extraction, namely 88.88% in the experiment with a NaOH concentration of 250 g/L, temperature of 100 oC, S/L ratio of 0.33 g/mL, leaching time of 40 minutes, and stirring speed of 400 rpm. Increasing the concentration of NaOH from 150 to 250 g/L increased the dissolution of Al, but tended to decrease if the concentration of NaOH was further increased. Increasing the temperature and leaching time, and decreasing the S/L ratio beyond the range tested, increased the dissolution percentage of Al. The synthesized FePO4 product obtained under optimum conditions had an average particle size of 413.6 nm and a Fe content of 29.03% (within the range of Fe content in commercial FePO4, namely 29-30%).