Abstract: The concentrator plant of Chengchao Iron Mine adopts magnetic separation followed by flo⁃ tation flowsheet to produce copper，iron，and sulfur concentrates. Thickeners with diameters of ϕ75 m， ϕ65 m，and ϕ30 m are used to treat different pulp streams. In view of the frequent problems of overflow turbidity and underflow density failing to meet requirements in each thickener，a systematic investigation was carried out on the thickening circuit. The feed properties，including chemical composition of the feed ore，pulp pH，apparent Zeta potential，feed solids concentration and fineness，as well as operating param⁃ eters such as thickener rake speed and throughput，were emphatically analyzed. The results show that the feed contains large amounts of calcium sulfate（gypsum）and chain and layer structured silicate minerals such as wollastonite and chlorite，which are prone to water absorption and sludging. The feed fineness se⁃ verely exceeds the design limit. The actual throughputs of the ϕ65 m and ϕ75 m thickeners exceed their design capacities，causing long term overloading. These factors collectively lead to reduced thickening effi⁃ ciency and overflow turbidity. It is recommended to strengthen pre classification before grinding，optimize grinding media to control over grinding，introduce flocculation sedimentation to enhance fine particle aggre⁃ gation，and upgrade the peripheral drive thickeners of ϕ75 m and ϕ65 m to central drive types to improve thickening performance.

Key words: thickener, process investigation, feed concentration and fineness, improvement measures