Factorial experiments for iron removal from kaolin by using single and two-step leaching with sulfuric acid

In the present study, to investigate the effects of acidic leaching on the iron removal from kaolin clay supplied by Cam-Ser Madencilik A.S., the 24 full factorial design of experiments and analysis of variance (ANOVA) were performed. The aim of the initial phase of research was to determine the effects of the main and interaction factors which can potentially influence the iron removal process. The factors were; pulp density, sulfuric acid concentration, temperature, leaching duration and reducing agent (oxalic acid, citric acid and hydrogen peroxide) concentration. The highest iron extraction yield (IEY) (26.3%) was obtained after 120 min of treatment at 90 °C, 20% pulp density, 3 M H2SO4 and with 0.50 M H2O2 as a reducing agent. For the purpose of increasing the IEY, in the second phase of research, initially the particle size of the kaolin sample was decreased to − 106 μm providing the liberation of iron oxides. Then, two-step leaching experiments were carried out with the optimum leaching conditions of full factorial design tests. The maximum IEY was 37.0% after two-step leaching with the optimum conditions of H2SO4 and H2SO4 with oxalic acid leaching. Iron oxide content of kaolin clay was decreased from 2.40% to 1.51%.

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► Treatment of kaolin containing high level of Fe2O3 with acid leaching.
► Full factorial design leaching tests; effects of main and interaction factors.
► Two-step leaching tests; increasing iron extraction yield (IEY).
► The highest IEY (%26.25) was obtained after H2SO4 leaching with H2O2.
► The IEY was increased to 36.95% after two-step leaching with optimum conditions.