Study on selective calcium removal by adsorption and gypsum precipitation control

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At Vale Long Harbour Processing Plant, nickel concentrate is leached using pressure oxidation process to**recover nickel, copper and cobalt, and lime is used to raise the pH of leach liquor to remove iron as precipitate.**Due to the high concentrations of calcium ion from the use of lime in iron removal process and sulfate ion in**the leach liquor, gypsum (CaSO4.2H2O) precipitate builds up very quickly in pipeline systems, resulting in**severe flow restrictions. To overcome the problem temporarily, the plant is in the process of building bypass**lines to allow cleaning the clogged main pipelines. It takes time, labour and money to clean pipelines with**gypsum scale. This is a serious process and technological problem they must solve for smooth and stable**production, especially in winter time when cold temperatures promote increased gypsum scaling rates.**The precipitation of gypsum is determined by the product of calcium ion concentration and sulfate ion**concentration in the processed system. In this project, we plan to solve or reduce the magnitude of the gypsum**fouling problem through selective calcium removal by adsorption using resins or other absorbents, or/and**controlled gypsum precipitation, i.e., accelerating gypsum precipitation in large volume tanks or thickeners,**which is much easier for gypsum cleaning and processing, before the solution with high concentrations of**calcium ion and sulfate ion enters to the pipeline systems. Engineering, environmental and economic factors**will be considered for process determination.**The accomplishment of this NSERC Engage program will help Vale Long Harbour Processing Plant maintain a**more stable and controllable nickel production process. The program is of great technological, economic and**social significances to Vale Long Harbour Operations and the Province of Newfoundland and Labrador.