Abstract: The circulating water of Limin Plant is rendered considerably high in concentration due to low slurry sedimentation efficiency. To address this issue, the overflow of the 1st-stage thickening pond is taken as the object of study and both its mineral and size compositions are analyzed. Based on the results of analysis, experimental study is conducted on the slurry sedimentation efficiencies that can be obtained in the case of using respectively the natural settling, flocculating settling and coagulating-flocculating settling methods. As revealed by study results, the plant's slurry water contains predominantely fine particles and high proportions of clay minerals like kaolinite, which is unable to meet the standard for use as circulating water solely through natural sedimentation; the use of cationic polyacrylamide PAM-1200 can accelerate slurry settling process and lead to improved water clarification result, and a highest slurry settling rate can be obtained when PAM-1200 is used at a concentration of 0.4% and a dosage of 8 g/t, and in this case, the supernatant has a turbidity as low as 75 NTU, making it possible for use as circulating water; the combined use of polymeric aluminium chloride(PAC) and PAM-1200 can lead to further improved slurry settling efficiency, and with the dosage of PAC at 8 g/t and a total dosage of the two agents at 108 g/t, the slurry can see a highest settling rate, allowing the turbidity of supernant to be further reduced to 38 NTU, a decrease of 37 NTU compared to the case of using PAM-1200 alone. It is demonstrated that when coagulant and flocculant are used in a mixed manner, the former's double-electric layer compression action coupled with the latter's bridging action can help accelerate slurry settling rate and hence improve slurry sedimentation result.