Abstract

The purification of a Chilean molybdenite concentrate containing 2.3 wt.% Cu as chalcopyrite was investigated to develop a low-temperature, cyanide-free process for selective copper removal. A chemical pre-treatment using NaCl and H2SO4 was applied, followed by leaching in a chloride-sulphate aqueous medium at 20 and 75 degrees C. The effects of sodium chloride dosage and wetting time during pre-treatment were evaluated under controlled leaching conditions (pH 1.5, 25 wt.% solids, 500 rpm, 48 h, and 70 g/L Cl-). Increasing both parameters promoted chalcopyrite decomposition into copper-iron oxides and sodium sulphide, while reducing elemental sulfur formation and enhancing crystallinity of the reaction products. These effects were attributed to the in situ generation of gaseous HCl during pre-treatment, which degraded chalcopyrite and reduced its refractoriness to subsequent leaching. The optimized condition (90 kg NaCl/t and 30 days of wetting, leached at 75 degrees C) reduced the copper content to 0.4 wt.% with no molybdenum dissolution, confirming selective copper removal through a non-oxidative mechanism. Kinetic analysis based on the unreacted shrinking-core model indicated a diffusion-controlled process through the pre-treatment reaction products, with an apparent activation energy of 13.6 kJ/mol. The proposed NaCl-H2SO4 pre-treatment provides a cost-effective and environmentally sustainable route for upgrading molybdenite concentrates in industrial applications. On a & eacute;tudi & eacute; la purification d'un concentr & eacute; de molybd & eacute;nite chilien contenant 2.3% en poids de Cu sous forme de chalcopyrite pour d & eacute;velopper un proc & eacute;d & eacute; & agrave; basse temp & eacute;rature et sans cyanure pour l'& eacute;limination s & eacute;lective du cuivre. On a appliqu & eacute; un pr & eacute;traitement chimique & agrave; base de NaCl et H2SO4, suivi d'une lixiviation en milieu aqueux de chlorure-sulfate & agrave; 20 degrees C et 75 degrees C. On a & eacute;valu & eacute; les effets du dosage de chlorure de sodium et du temps de mouillage lors du pr & eacute;traitement, dans des conditions de lixiviation contr & ocirc;l & eacute;es (pH 1.5, 25% en poids de solides, 500 tr/min, 48 h et 70 g/L Cl-). L'augmentation des deux param & egrave;tres a favoris & eacute; la d & eacute;composition de la chalcopyrite en oxydes de cuivre et de fer et en sulfure de sodium, tout en r & eacute;duisant la formation de soufre & eacute;l & eacute;mentaire et en am & eacute;liorant la cristallinit & eacute; des produits de r & eacute;action. On a attribu & eacute; ces effets & agrave; la g & eacute;n & eacute;ration in situ de HCl gazeux lors du pr & eacute;traitement, ce qui a d & eacute;grad & eacute; la chalcopyrite et r & eacute;duit sa r & eacute;fractarit & eacute; lors de la lixiviation ult & eacute;rieure. Les conditions optimales (90 kg NaCl/t et 30 jours de mouillage, lixiviation & agrave; 75 degrees C) a r & eacute;duit la teneur en cuivre & agrave; 0.4% en poids sans dissolution du molybd & egrave;ne, confirmant l'& eacute;limination s & eacute;lective du cuivre par un m & eacute;canisme non oxydatif. L'analyse cin & eacute;tique, bas & eacute;e sur le mod & egrave;le du c oe ur r & eacute;tr & eacute;cissant non r & eacute;agi, a indiqu & eacute; un proc & eacute;d & eacute; contr & ocirc;l & eacute; par diffusion & agrave; travers les produits de la r & eacute;action de pr & eacute;traitement, avec une & eacute;nergie d'activation apparente de 13.6 kJ/mol. Le pr & eacute;traitement NaCl-H2SO4 propos & eacute; offre une voie rentable et respectueuse de l'environnement pour la valorisation des concentr & eacute;s de molybd & eacute;nite dans les applications industrielles.