Heavy metal removal from dredging slurry using a parabolic hydrocyclone

Abstract

Heavy metals usually aggregate as fine particles in dredging slurry and need to be removed or reduced before recycling of the slurry. However, traditional hydrocyclone method often leads to low separation efficiency because of the difficulties in the complete separation of fine particles. To address this problem, this paper proposes a new type of parabolic hydrocyclone for the removal of heavy metals from dredging slurry. The computational fluid dynamics (CFD) software together with mixture and Reynolds stress model (RSM) have been used to simulate the internal flow field of the parabolic hydrocyclone, which was then verified with experimental tests. The simulation results show that, compared with traditional hydrocyclones, the flow field inside the parabolic hydrocyclone is more stable, which effectively help to avoid the mixture of coarse and fine particles caused by the flow field disturbance. Further experimental results demonstrate that the cumulative percentage of fine particles in the underflow product decreases. The cut size increases from 30 μm to 49 μm and the steepness index rises from 0.13 to 0.2, which proves that the separation accuracy can be improved, and the fine particles mixed in the underflow can be removed effectively. Moreover, the recovery rate of heavy metalas Zn and Cr in the overflow products reaches 97.21 % and 78.27 %, respectively, verifying the enrichment effect. Therefore, after the parabolic hydrocyclone separation process, the underflow products contain less heavy metals and become both non-hazardous and recyclable.