To rationally select parameters for pipeline transportation of ultra-fine tailings slurry, the influencing factors of pipeline resistance in transportation were classified based on theoretical analysis. Effects of different factors on resistance loss in ultra-fine tailings slurry pipeline were investigated by adopting response surface methodology (RSM), and the significance of each factor was obtained, for which engineering verification test was performed then. The results show that those three internal influencing factors, such as slurry concentration, slurry temperature and cement-sand ratio, are in descending order of sensitivity, and the interactions among them, including interaction between concentration and temperature of slurry, interaction between slurry concentration and cement-sand ratio, interaction between cement-sand ratio and slurry temperature, are also in descending order of sensitivity; while the external factors, such as pipe diameter, flow rate and stowing gradient, and their interaction, including interaction between pipe diameter and inlet flow rate, interaction between pipe diameter and stowing gradient, interaction between inlet flow rate and stowing gradient, are also in descending order of sensitivity. The factor optimization results indicate that with fixed external factors, the optimal combination of slurry properties are as follows:slurry concentration of 63.5%, cement-sand ratio of 1∶6, and slurry temperature of 51.5 ℃; while with fixed internal factors, the optimal combination of transportation parameters are as follows:pipe diameter of 270 mm, inlet flow rate of 1.63 m/s, and stowing gradient of 5. Based on verification test, it is found that the maximum calculation deviations of the confidence interval under the influences of internal and external factors are 10.82% and 3.41%, respectively.

To investigate the dynamic damage characteristics and energy evolution of sandstone in aquatic environments after engineering disturbance and blasting vibration, a split Hopkinson pressure bar (SHPB) was used to test three groups of saturated and dried sandstone with different initial damages. A statistical damage constitutive model was established by introducing initial damage and degree of saturation, which was then used in combination with damage curves to analyze the whole-process damage mechanism of sandstone with initial damage. It is found that the stress-strain curve of sandstone can be divided into four parts based on energy evolution. After reaching peak stress, things change. Elastic energy begins to release and a significant energy hysteresis phenomenon occurs throughout the failure process. At the same strain rate, the degree of fragmentation gradually increases as the initial damage becomes greater and sandstone is more saturated. The theoretical stress-strain curve of the modified damage constitutive model is in better coincidence with the practical one, presenting the highest correlation coefficient (0.991). The mechanism for whole-process sandstone damage can be characterized by the established damage curves. Furthermore, the initial damage and saturation-induced damage of sandstone are equivalent to its load-induced damage to a certain extent.

An experimental study was carried out on comprehensive recovery process for the gold-cobalt polymetallic copper ore in Bolivia. A flow sheet of Cu-preferential flotation followed by bulk Au-Co-Bi flotation was adopted, with OL-ⅡA as a Cu collector and OL-TL as a depressant. The Cu-preferential flotation process consisting of one stage of roughing, two cleaning and one scavenging produced a copper concentrate grading 30.00% Cu at 94.56% recovery, indicating separation between copper and arsenopyrite actualized by low-alkalinity flotation. Then, the obtained tailings were subjected to a bulk Au-Co-Bi flotation consisting of one stage of roughing, one cleaning and one scavenging, resulting in a Au-Co-Bi concentrate grading 19.50 g/t Au, 1.58% Co and 1.80% Bi, with corresponding recoveries of 92.22% Au, 96.33% Co and 58.87% Bi. It is concluded that the comprehensive recovery of metallic resources can be actualized from this gold-cobalt polymetallic ore.

As for the high-calcium silver-vanadium ore from Yichang of Hubei Province, which has low grades of silver and vanadium but high content of calcium, the feasibility of removing calcium-bearing minerals therein, predominantly dolomite, by reverse flotation was explored through experiments, and the effects of grinding fineness, type and dosage of depressant, pH of pulp and collector dosage on decalcification and vanadium recovery were investigated. The results show that with grinding fineness of-0.074 mm 77.19%, sodium silicate, sodium oleate and sodium carbonate at dosage of 400 g/t, 800 g/t and 1 500 g/t, respectively, a closed-circuit reverse flotation test can produce a vanadium concentrate grading 1.04% V₂O₅ at 93.56% recovery, with CaO content of 3.37%. It is shown that the calcium-bearing minerals have a CaO grade of 27.55%, showing CaO removal rate reaching 85.34%.

To explore the feasibility of using nano-ceramic balls in primary ball mill, a ball milling test was conducted on high-pressure roller mill product with steel balls and nano-ceramic balls as grinding media, and the particle size distribution characteristics and magnetic separation effect of the ground products were studied. The results indicate that with the feed materials singly in a size range of 2-3 mm or 1-2 mm, use of nano-ceramic balls in combination with steel balls as the medium can reduce the overall grinding effect; while with the feed material singly in a size range of 0.6-1 mm, 0.3-0.6 mm, 0.15-0.3 mm or 0.074-0.15 mm, a combination of nano-ceramic balls and steel balls has a synergistic effect, which can enhance grinding performance; with the feed material singly in a size range of 0.3-0.6 mm, 0.15-0.3 mm or 0.074-0.15 mm, the mixed media with 50% steel balls can achieve the same grinding effect brought by the media with 80% steel balls; with the feed material in a size range of 0.074-0.15 mm, the combination of two balls brings the same grinding effect as the single use of steel balls; with the feed material in a size range less than 0.6 mm, the combination of two balls can bring grinding effect approximately equivalent to that by singly using steel balls. It is concluded that a combination of nano-ceramic balls and steel balls can be used instead of single steel balls in the primary grinding of materials in size range less than 0.6 mm.

In order to improve recoveries of rare earth resources, Bayan Obo rare earth ore was taken for research, for which a combined process consisting of XRF sorting, low-intensity magnetic separation (LIMS) and flotation was adopted to recover rare earth elements (REEs )and iron minerals therein. With appropriate parameters, a rough concentrate of rare earth was obtained with a REE grade of 9.44%, recovery of 94.03% and an enrichment ratio of 1.48, and the tailings for discarding had a REE grade of 1.03%, presenting a discarding rate of 5.97%. After that, a process consisting of LIMS and flotation was adopted, producing a rare earth concentrate grading 61.23% REE at 79.81% recovery, with a yield of 19.89%, and the tailings with iron grade of 58.68% at 83.27% recovery. It is concluded that such processing technique can improve the REE grade of the feed into the mill and also simplify the flotation flowchart, providing a new idea for efficient recovery of rare earth ore.

A high-pressure grinding roll (HPGR) was adopted for dry milling of the weakly magnetic iron ore from Jingtieshan prior to magnetizing roasting. The results indicate that compared to wet milling, the dry milling process can reduce production costs and energy consumption. The extrusion pressure of the HPGR exerts a direct impact on the shape of the obtained cake and the subsequent breaking process. In contrast to single extrusion, multiple extrusions lead to a significant reduction in power consumption of the main machine. With the pressure of 4 MPa, the final powder with approximately 53% of passing size of-0.074 mm will require the main machine with power consumption of 6.74 kWh/t, and a circulating load of about 330%. It can meet the requirement of particle size for the subsequent roasting process.

An experimental research on co-enrichment and recovery of multiminerals by flotation process was conducted for a lithium-niobium-tantalum-beryllium polymetallic ore in Western Sichuan. By adopting a process consisting of direct grinding and bulk flotation with self-developed EM-PN30 as a collector, a closed-circuit test produced a lithium-niobium-tantalum-beryllium concentrate grading 5.60% Li₂O, 0.035% Nb₂O₅, 0.015% Ta₂O₅ and 0.138% BeO, with Li₂O recovery of 85.98% and recoveries of other associated niobium, tantalum and beryllium at 73.13%, 78.33% and 52.58% respectively. It is concluded that a comprehensive enrichment and recovery of lithium, niobium, tantalum and beryllium from such polimetallic ore can be actualized, which can provide favorable conditions for the subsequent Nb/Ta separation and Li/Be separation by magnetic or gravity separation process.

Based on beneficiation tests of a low-to-medium grade magnetite-hematite ore, a combined processing technique was developed, consisting of high-pressure roller grinding, preconcentration with low-intensity magnetic separator, staged grinding - staged separation and magnetic elutriation of preliminary concentrate, and high-intensity magnetic separation and gravity separation of preconcentration tailings. It is shown that the preliminary concentrate from preconcentration process is subjected to staged grinding and staged separation, followed by magnetic elutriation, resulting in a magnetite concentrate grading 70.57% TFe at 67.25% recovery, with total content of SiO₂ and Al₂O₃ less than 3%. The tailings from preconcentration then go to flat-ring high-intensity magnetic separator followed by gravity separator, generating hematite grading 63.52% TFe at 16.61% recovery. The recovery from the whole process is totally 83.86%.

Aiming at the problems of high oxidation rate, high content of slime and high consumption of collector (butyl xanthate) for the copper-cobalt oxide ore from the Democratic Republic of the Congo, experimental researches were carried out with an auxiliary collector (MC-07) in its flotation process. The results show that at the stage of copper oxide ore flotation, with butyl xanthate as a single collector at a total dosage of 400 g/t, the concentrate is produced totally with a copper recovery of 78.41% and a cobalt recovery of 38.93%; while by using the conventional collector of butyl xanthate in combination with an auxiliary collector of MC-07, at the dosage of 99 g/t and 33 g/t respectively, the concentrate is finally produced totally with a copper recovery of 78.76% and a cobalt recovery of 39.30%. It is shown that small additions of auxiliary collector of MC-07 can reduce the dosage of butyl xanthate with the similar technical indicators.