Technico-economic simulation for the HCl-leaching of hybrid serpentine andmagnesite feeds

A flexible technico-economic computer model was developed to minimize the o perating cost of the HCl-leach of mixed feeds consisting of serpentine and magnesite ores in a magnesium electrolytic reduction plant. A complete mass balance was first established for HCl-leaching and filter cake washing by taking into account such process variables as the extent of MgO extraction from serpentine ore, pulp density of leach slurry, MgCl2 concentration of f iltrate, moisture content of filter cake and degree of cake washing by disp lacement and diffusion mechanisms. A mathematical model was then built by c ombining the mass balance with the costs of serpentine ore preparation, fil tration, brine evaporation and waste wet cake disposal as well as the price s of magnesite ore, hydrochloric acid and electricity. The model includes t he capital and operating costs of hydrometallurgical processing from ore pr eparation to the production of magnesium chloride hexahydrate MgCl2. 6H(2)O . The technico-economic simulation model shows that when the respective cos ts of serpentine and magnesite ores are $15/t and $90/t, the lowest product ion cost of hexahydrate can be achieved with a leach-feed of about 65% serp entine and 35 % magnesite, and by washing the filter-cake with hot water ha ving a volume 1.3 times that of the occluded brine.