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A STUDY OF HYDROMETALLURGICAL TREATMENT OF COMPLEX SULPHIDE ORES BY LEACHING WITH FERROUS CHLORIDE AND OXYGEN IN A HIGHLY CONCENTRATED AMMONIUM CHLORIDE AQUEOUS SOLUTION.

Obiettivo

TO STUDY A PROCESS FOR THE TREATMENT OF BULK CONCENTRATES OF COMPLEX SULPHIDES.
The present invention is related to a process for the recovery of zinc, copper and lead from different raw materials by leaching with a concentrated ammonium chloride solution, which will generate the equivalent metal amines. The separation of copper and zinc from the pregnant solution is performed by organic acid extractants (cationic and/or chelating extractants), which are neutralised by the already existing amines, regenerating the original ammonium chloride solution. Copper and zinc which have passed into their respective organic phases, are stripped with the sulphuric acid produced in the electrolysis of the corresponding loaded electrolyte. Lead is removed by crystallization as lead chloride.

The objective of the research was the study and development of a process for the treatment of bulk concentrates of pyritic complex sulphide ores. The process was based on an oxidizing leaching in a highly concentrated ammonium chloride aqueous solution using oxygen as oxidizing agent. The study comprised the solubilization of metal values by a double step leaching, as well as the pregant solution treatment for their recovery. Based on the experimental data, the process simulationand its economical evaluation were performed.

The knowledge about the reaction mechanisms, solubility diagrams and equilibrium conditions of the different steps of the process is now complete and the behaviour of the 3 different bulk concentrates as a function of the experimental conditions is known and may be extrapolated for other similar materials. This has led to the establishment of a hydrometallurgical process diagram for the treatment of complex sulphides.

The developed process is specially appropriate for the treatment of polymetallic complex sulphides giving:
high recovery yields for zinc, copper, lead and silver (over 95%);
mild operating conditions appliled for leaching steps;
very pure solutions during the leaching;
natural regeneration of leaching solution for metal value recoveries;
no losses of lead and silver occur as jarosites.

As a complement to the development of a new process for the recovery of nonferrous metals, a profitability study was conducted in an attempt to reveal. In economic terms, the addressing 2 different types of concentrates, the Aljustrel Portuguese concentrate and the Aznalcollar Spanish concentrate. The estimated profitability indices while showing a better performance from the Spanish concentrate, also suggested a marginal advantage from the Portuguese concentrate due to incremental plant capacity and electricity charges.
THE RESEARCH IS COMPOSED OF THE FOLLOWING PHASES :
1. LEACHING :
- STUDY OF THE LEACHING OF THE BULK CONCENTRATES OF THREE DIFFICULT AND COMPLEX ORES.
- STUDY OF THE LEACHING RESIDUES.
- REMOVAL AND RECOVERY OF SULPHUR.
- STUDY OF THE RATIO CU+/CU+ DURING THE LEACHING AND OXIDATION PREVIOUS TO CU++ SOLVENT EXTRACTION.

2. TREATMENT OF SOLUTIONS :
- SEPARATION OF LEAD BY CRYSTALLISATION OF CL2PB.
- REMOVAL OF CU BY SOLVENT EXTRACTION WITH LIX-65N.
- REMOVAL OF ZN BY SOLVENT EXTRACTION WITH DEHPA.
- REMOVAL OF SILVER BY CEMENTATION.

3. STUDY OF THE TOAL PROCESS :
- STUDY OF THE PROCESS IN A CLOSED CIRCUIT WITH RECYCLING SOLUTIONS.
- SIMULATION OF THE PROCESS.
- EVALUATION OF TOTAL PROCESS.

THE PROCESS HAS A GREAT DEAL OF NOVELTY AND IT IS PROTECTED BY THE SPANISH PATENT NO 545.698 (1985). IT PRESENTS CERTAIN ADVANTAGES OVER ALL KNOWN PROCESS, NAMELY:
- A UNIQUE STEP OF SOLUBILISATION FOR ALL NON-FERROUS METAL VALUES (CU, ZN, PB, AG) AVAILABLE AS FAR AS ITS CONTENT OR ITS PRICE WILL BE OF INTEREST TO RECOVER;
- TO OBTAIN IRON-FREE SOLUTIONS, WHICH FACILITATE SUBSEQUENT REMOVAL OF EACH METAL VALUE;
- MINOR IMPURITIES IN ORE, SUCH AS SN, BI, SB, HG, REMAINING IN THE LEACHING RESIDUE AND ONLY GO INTO LEACHING SOLUTION AT LEVEL OF FEW P.P.M. THIS LEADS TO BETTER QUALITY PRODUCTS OR TO A LOWER COST TO OBTAIN THEM;
- TO OBTAIN A SOLUTION WITH A RELATIVELY HIGH CONCENTRATION OF METALS (1 MOL/LITER OF CU+ZN+PB), WHICH ALLOWS A FAVOURABLE UNITARY COST;
- RECYCLING AND REGENERATION OF SOLUTIONS, WHICH HAS A REPERCUSSION OF A MINIMUM REAGENT CONSUMPTION.

THE PROCESS MAY BE VERY IMPORTANT FOR THE EXPLOITATION OF THE LARGE DEPOSITS OF COMPLEX SULPHIDES EXISTING IN SPAIN AND PORTUGAL, IN WHICH THE NON FERROUS METAL SULPHIDES ARE FOUND FINELY DISPERSED WITHIN THE PYRITIC MATRIX WITH A HIGH DEGREE OF ASSOCIATION.

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NATIONAL LABORATORY FOR ENGINEERING AND INDUSTRIAL TECHNOLOGY
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