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The deformation properties of cemented tailings backfill (CTB), especially prepared from sulphidic tailings, are valuable for the estimation of design parameters for underground stope filling as well as for numerical simulation. In this paper, the effect of curing time, sulphur content, cement dosage and solids concentration on the free expansion ratio of CTB specimens was investigated using an invented lab apparatus called "free expansion measuring instrument". The backfill recipe (sulphur content, binder dosage and solids concentration) and curing days had significant influences on the expansion performance of the CTB. The results indicated that with the change of sulphides, the free expansion ratio (FER) showed no obvious growth at the curing of 28 days. However, after the curing of 120 days, FER increased from 4.96% (S: 4%) to 9.61% (S: 20%). As the solids concentration increased, the FER also rised. And this growth was distinctive only when the solids concentration is relatively high (65~75%) and at the long-term curing time (120 days). The proportions of binder and the obtained FER clearly show a sub-linear and proportional relationship. Increasing the amount of binder (8~16%) could not restrict the increment of expansion ratio, and ultimately the CTB specimens would generate cracks and collapse.

Gravity thickening is an important aspect to solve numerous environmental and safety problems that were created by tailings discharging at low solid concentrations. Furthermore, in order to efficiently facilitate the separation of released water and solid sediments, a continuous thickening system with ultrasonic equipment has been used to investigate the thickening performance of copper-mine tailings under different ultrasonic frequencies (16 kHz, 20 kHz, 22 kHz, 25 kHz, and 28 kHz). After freeze-drying treatment, the underflow samples are imaged using the scanning electron microscope (SEM); then, the structure of floc or aggregates in the SEM images is quantifiably analyzed using the software of Image J. Results show that the underflow concentration increases as the ultrasonic frequency increases and decreases afterwards. A linear logarithmic function can explain the relationship between underflow concentration and run time at a certain ultrasonic. The underflow concentration is maximized at 64.47 wt. % when the ultrasonic frequency is 22 kHz. Based on the analysis on the microstructure of underflow samples, the minimum pore average size and pore average fraction are obtained when the ultrasonic frequency is 22 kHz, implying that 22 kHz is the optimum ultrasonic frequency combining the results of the underflow concentration.