Abstract Silicon represents about 50% of the price of photovoltaic generation systems; shortages in silicon negatively affect the photovoltaic generation industry and there is no reason for those effects not to continue. The development of a recycling technology for silicon waste, such as the waste sludge from silicon wafer back grinding, is important for easing the demand for silicon material. The back grinding (thinning) of silicon wafers produces a large amount of silicon waste sludge and the amount is continually increasing due to the demand for thinner semiconductor wafers. Wafer back grinding waste is mainly a slurry of silicon and abrasive alumina (Al 2 O 3 ) particles. Although the silicon particles retain their high purity, they have not been successfully recycled from the slurry for reuse. There is generally a lower alumina content than that of silicon and the particles are of the micron or submicron order. Due to their small size, and because their weight is similar to that of silicon, high-gravity centrifugation is not an effective removal technique. Previously, the properties of silicon sludge were analyzed and applied to the wet classifier system for recycling pre-processing of recycling, however, inductively coupled plasma mass spectrometry showed that the purefied silicon powder contained iron, aluminium, copper and natrium. The density of the hot-pressed sample was 94% higher than that of the spark plasma sintering sample. The bulk density was measured and compared to theoretical density of silicon as determined by Archimedes’ density measurements. The separation effects on silicon sludge, powder purity, consolidation, and the properties of the resulting silicon wafers were investigated.