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Study of column leaching of laterites

Tsoukalou Amalia

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Summary

Leaching is a hydrometallurgical process which has the aim of selective dissolution of useful metals from an ore, using aqueous solutions. Nickel (Ni) found in lateritic ores is a quite important metal and has a wide range of properties. Thus, many investigations for the economic extraction of nickel using pyrometallourgical or hydrometallurgical processes have been carried out so far. However, due to the high energy requirements of pyrometallourgy, research efforts are focusing on the development of more economical and eco-friendly hydrometallurgical approaches.Laboratory investigation of nickel extraction involves column leaching, a process which simulates heap leaching. Heap leaching is a hydrometallurgical process for extracting useful metals mainly from low-grade ores.In this thesis, column leaching tests of nickeliferous laterite ores from the areas of Kastoria and Agios Ioannis (Viotia), Greece, were carried out. Kastoria ores are of saprolitic (with high MgO content > 25% and low Fe content < 12%) while Agios Ioannis ores are of limonitic type (with low MgO < 10% content and high Fe, 15-32% or >32%). The investigation involves six tests under different leaching conditions. More specifically, three column leaching tests for each laterite were conducted in laboratory leaching columns (diameter of 5 cm and length of 50 cm). The bed consisted of 1000 g ore and the leaching solution used was either sulfuric acid (strength of 1N or 3N) or hydrochloric acid (strength of 1N). Upflow transport of the acid solution with the use of peristaltic pumps at a constant rate (3.5 L/day for Kastoria laterite and 10L/day for Agios Ioannis laterite) was considered and the pregnant leach solution (PLS) was recycled several times. Samples from the outflow were taken at predetermined time intervals to determine the concentration of Ni, Co, Fe, Ca, Al, Mg and Mn by Atomic Absorption Spectroscopy (AAS).The experimental results showed that Ni and Co extraction from Kastoria laterite with the use 1N H2SO4 reached 16% and 13%, respectively. The use of 1N hydrochloric acid (HCl) resulted in 12% and 10% extraction of Ni and Co, respectively. Strongest acid solution (3N H2SO4) resulted in higher extractions of both metals (50% for Ni and 30% for Co).Regarding Agios Ioannis laterite, the results showed that Ni and Co extraction with the use 1N H2SO4 reached 40% and 55%, respectively. The use of 1N hydrochloric acid (HCl) resulted in 28% and 49% extraction of Ni and Co, respectively. Strongest acid solution (3N H2SO4) resulted in higher extractions of both metals (65% for Ni and 71% for Co).

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