Solid-liquid separation of metal sulfide precipitates is a key unit operation in hydrometallurgical processing and in mining-related process water treatment, where efficient metal recovery and production of clear filtrates are essential for downstream operations. This study investigates the vacuum filtration performance and cake properties of metal sulfide precipitates formed from a multicomponent sulfate solution, with emphasis on the effects of vacuum level and slurry solid content on filtration behaviour, cake resistance, porosity, and filtrate clarity.

A synthetic metal-bearing solution containing CaSO₄·2H₂O, CoSO₄·7H₂O, CuSO₄·5H₂O, MgSO₄·7H₂O, MnSO₄·H₂O, Na₂SO₄·10H₂O, and ZnSO₄·7H₂O was prepared to simulate the composition of a process side stream from a commercial cobalt processing plant in Finland. Sulfide precipitation was carried out in a jacketed glass reactor at 60 °C using sodium hydrosulfide (NaHS), with the sulfide dosage selected based on a Cu:S molar ratio of 1:2.4 to ensure complete copper sulfide precipitation. The precipitated slurry was filtered using a Buchner funnel mounted in a sealed vacuum chamber, allowing precise control of the pressure drop across the filter cake. Filtration experiments were conducted using two slurry masses (300 g and 500 g) at three vacuum levels (0.3, 0.5, and 0.7 bar). Filtration data were used to determine the average specific cake resistance (α_av), cake porosity (Ɛ_av), and filtrate turbidity as measures of separation performance [...]