Pasivizacija halkopirita tokom luženja rastvorom sumporne kiseline u prisustvu natrijum-nitrata

Abstract

U radu su prikazani rezultati ispitivanja luženja halkopiritnog koncentrata rastvorom sumporne kiseline u prisustvu natrijum-nitrata. Izračunate standardne vrednosti Gibsove energije reakcija luženja i analiza E-pH dijagrama stabilnosti potvrdili su mogućnost luženja bakra i železa iz halkopiritnog koncentrata u ispitivanim uslovima. U oksidacionim uslovima pri niskoj vrednosti pH bakar prelazi u rastvor kao Cu2+, a železo kao Fe2+ i Fe3+. Rendgenska difrakciona i termijska analiza (TG/DTA) čvrstih ostataka dobijenih pri različitim uslovima luženja, pokazuju prisustvo halkopirita i elementarnog sumpora, čime je potvrđeno predviđanje da se sulfidni sumpor oksidiše do elementarnog oblika. Skenirajućom elektronskom mikroskopijom (SEM/EDX) utvrđeno je da se nastali sumpor taloži po površini halkopiritnih mineralnih zrna i usporava reakciju u kasnijoj fazi luženja. Taloženjem sumpora dolazi do promene mehanizma procesa iz kinetičkog u difuziono kontrolisani.

In this work, the process of the chalcopyrite leaching in sulphuric acid solution was investigated. Sodium nitrate was used as oxidant in the leaching process. Chemical reactions of leaching and their thermodynamic possibilities are predicted based on the calculated Gibbs energies and analysis of E-pH diagrams. The negative values of the Gibbs energy show that all chemical reactions are thermodynamically feasible at atmospheric pressure and in a temperature range 25-90°C. At high electrode potential and low pH values, Cu2+, Fe2+ and Fe3+ exist in water solutions. The increase of temperature reduces the probability of Fe3+ existence in the system. The chalcopyrite concentrate, enriched in the 'Rudnik' flotation plant, with 27.08% Cu, 25.12% Fe, 4.15% Zn and 2.28% Pb was used in the work. XRD and DTA analysis of the concentrate reveals that the sample contains mainly the chalcopyrite with small amount of sphalerite. For the description of the reaction of leaching process the leach residuals, obtained at different conditions, were chosen for XRD, TG/DTA and SEM/EDX analyses. The elemental sulphur and chalcopyrite phases identified in leach residuals confirm our prediction that the elemental sulphur is formed during the leaching process. Accordingly, elemental sulphur is the main product of the reaction, while a minor amount of sulphide sulphur is oxidized to sulphate during the leaching. The sulphur formed during the reaction was precipitated at the particle surfaces, and slowed down the leaching rate in the final stage of leaching process. In the initial stage, the reaction rate was controlled by the surface reaction. The mechanism, latter has been changed into a diffusion controlled one.