Abstract: In order to improve phosphorus selection effect，the slime，which is ultrafine and difficult⁃ ly to settle was produced by cyclone before flotation in Gafsa phosphate washing plant of Tunisia. The slime was described with pH of 7，dry density of 2.86 g/cm³ and yield of -23 μm grain size of 65.2%.In or⁃ der to solve the problem of high efficient settlement of the slime，a systematic dense settlement test was car⁃ ried out. The results showed that: ①The static natural settlement test showed that the natural settlement ve⁃ locity is very slow regardless of the pulp concentration. The lower the concentration is，the faster the sedi⁃ mentation rate is.The amount of dry ore treated per unit area at different concentrations is almost un⁃ changed. ② The static flocculation settlement test showed that the sedimentation rate is significantly accel⁃ erated with the addition of flocculant TNS，and sedimentation rate is faster with the increase of TNS dos⁃ age，and the dry ore treatment capacity per unit area increases correspondingly. The higher the pulp concen⁃ tration is，the slower the sedimentation rate is，and the dry ore treatment capacity per unit area increases first and then decreases.The appropriate pulp concentration is 5%.③The dynamic flocculation settlement test showed that the concentration of underflow decreases and the concentration of overflow water increases with the increase of slurry feeding speed. In order to ensure that the underflow concentration is higher than 25%，the suitable feeding speed of dynamic thickening test device is determined to be 0.1 m³/h.

Key words: phosphate ore, slime, thickener, settlement, flocculant TNS