NATIONAL TECHNICAL UNIVERSITY OF ATHENS
SCHOOL OF MINING AND METALLURGICAL ENGINEERING
Section of Metallurgy and Materials Technology
Laboratory of Metallurgy
 
HYDROMETALLURGY UNIT
 
 
Indroduction
 

The Laboratory of Metallurgy of the National Technical University of Athens developed and patented long ago a novel integrated hydrometallurgical method, the HELLAS (Heap Leach LAteriteS) Method, suitable to treat low grade nickel oxide (laterite) ores efficiently and economically. The method involves:

  • Heap leaching of the ore with dilute sulphuric acid at ambient temperature
  • Removal of iron, aluminium and chromium from the pregnant leach solution by chemical precipitation, at atmospheric pressure, as easily filterable crystalline basic sulphate salts of jarosite –alunite type.
  • Solvent extraction of cobalt, manganese and magnesium over nickel using Cyanex 272, at certain conditions, and stripping of the loaded organic phase with sulphuric acid solution.
  • Nickel concentration in the raffinate by solvent extraction with Cyanex 272 at certain conditions.
  • Nickel electrowinning from the concentrated raffinate, using stainless steel as cathode and Pb-8% Sb as anode.
  • Solvent extraction of cobalt and manganese over magnesium using Cyanex 302, at certain conditions, and stripping of the loaded organic phase with dilute sulphuric acid solutions.

  • Removal of magnesium by chemical precipitation at ambient temperature, using Ca(OH)2 as the neutralizing agent. The produced mixed precipitate, composed of well – crystallized gypsum (CaSO4. 2H2O) and aggregates of fine crystallites of brucite (Mg(OH)2), exhibits excellent filtering properties.

The heap leach technique was applied to nickel oxide ores (laterites), after a suitable and very simple pretreatment of the ore with water, by the Research Group of the Laboratory of Metallurgy, N.T.U.A, for the first time worldwide.

The construction and operation of the pilot plant to heap leach low grade laterites, using the HELLAS Method, were performed in the framework of a research project entitled “Innovative Technologies – Techniques for the Evaluation and Exploitation of Metalliferous Minerals”. This project was financed by the Ministry of Development - Institute of Geology and Mineral Exploration (I.G.M.E.) and supervised by Mr. Jack Drougas, Director of I.G.M.E.

The heap was designed by the N.T.U.A. Research Group and constructed by the General Mining and Metallurgical S.A. LARCO. The pilot -scale heap leach test was performed by the N.T.U.A. Research Group assisted by personnel of I.G.M.E.