Current Journal of Applied Science and Technology

The growth of mining activities, together with recent tailings dam failures, has increased the need to evaluate alternative methods for the disposal of tailings and other by-products generated during mineral processing. In this context, dewatering represents an important strategy for enabling alternative disposal methods, such as filtered tailings stacking. This study investigated the filtration dewatering behaviour of phosphate tailings and the effects of flocculant type, pH, and dosage on cake moisture content and unit filtration rate (UFR). Preliminary vacuum filtration tests were conducted to establish the dewatering time and screen commercial reagents for the subsequent experiments. Magnafloc 351, a nonionic polyacrylamide, and Magnafloc 504, a cationic polyacrylamide, were selected and evaluated using a 2³ full factorial design with duplicate experiments. Laboratory-scale vacuum filtration tests were performed with phosphate tailings slurries containing 60 wt. % solids. The target cake moisture content for subsequent compaction and stacking was established at 11.59% on a wet basis based on the Proctor compaction test. Factorial analysis showed that flocculant dosage had the largest effect on cake moisture content, whereas pH had the strongest effect on UFR, with significant interactions among the experimental factors. The best overall compromise between residual cake moisture and filtration rate was obtained with Magnafloc 351 at pH 6 and a dosage of 30 g/t, resulting in a cake moisture content of approximately 17.25% and a UFR of 387 kg/m² h. Although the target moisture content was not achieved, the results demonstrate that flocculant characteristics and operating conditions strongly influence phosphate tailings filtration and that conditions favouring higher filtration rates do not necessarily minimise residual cake moisture.