Causes and prevention of irrigation blockages in the bioleaching process
Case study: Terrafame mine
W. Strycharski (TU Delft - Civil Engineering & Geosciences)
T.J. Heimovaara – Mentor
D.J.M. Tillard – Graduation committee member
Doris van Halem – Graduation committee member
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Abstract
Blockages in irrigation during bioleaching operation cause additional production costs and might negatively influence metals yield. The main research question was to find out if the lifetime of the irrigation system can be extended. Production process was investigated from various angles in search of causes and patterns of solution flow blockages due to calcium sulfate precipitation which was identified as the main reason of clogging. Large number of process data was statistically analyzed. Clear correlation between the PLS temperature and calcium concentration in the solution was drawn and it was found that it is far different from any other research presented. Calcium solubility was experimentally tested – solution was cooled down to approx. 4 °C and agitated daily. Results were unclear, however, on average, calcium concentration decreased by approx. 100 mg/L. The ambiguity of the initial solubility trials led to designing a new experiment. Investigation of the system pointed out critical points and allowed for the formulation of clogging control strategy. Primary calcium sources were found within the ore and metals recovery plant; sulfate is produced during bioleaching process and added to the solution with sulfuric acid – pH control. Forced precipitation of gypsum was proposed as the most viable solution. Conceptual precipitation pond was proposed based on seeded batch crystallization of gypsum. Moreover, clogging was found more prominent in areas with lower pressure head thus redesigning of the irrigation system was suggested along with implementing pulsating pressure. The outcomes of this study set a new direction for the company to counter calcium precipitation problem.