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Traditional paste filling materials adopt industrial solid wastes such as unclassified tailings and waste rocks as filling aggregates, but the binder used is dominantly commercial cement, which raises the filling cost. Hemihydrate phosphogypsum (HPG) is one of the main by-products of the phosphorus chemical industry, and the high-efficiency utilisation technology of HPG has been a problem worldwide. The potential gelling property of HPG is found in the laboratory at first. It is then modified by appropriate chemical and physical methods to produce new filling binder with the purpose of replacing cement completely. A lot of experiments show that the modified HPG (MHPG) has outstanding properties of quick setting (setting time less than 90 minutes), high early strength (UCS for three days more than 8 MPa) and good flowability (yield stress less than 50 Pa). In addition, MHPG can bind different aggregates according to the filling needs to prepare a homogeneous, non-settling, and non-bleeding filling paste. In the past three years, two mines in Guizhou, China have adopted the underground paste backfill technology and surface open pit cemented filling technology based on MHPG paste materials. In practice, this new technology reduces the material cost by 30%, increases the flow capacity by 50%, and has a solid wastes rate of more than 98% compared to traditional methods.

Friction losses is a key parameter in the design of pipeline transportation in paste backfill. A full-scale pipeloop test was conducted in the JCHX Paste Backfilling laboratory to investigate the friction losses of cemented unclassified iron tailings slurry. Friction losses in upward sloping pipe, vertical downward pipe, vertical upward pipe, 90° long radius elbow, horizontal straight pipe and downward sloping pipe were tested simultaneously under different solid fractions. The results indicated that friction losses always increase with flow rate and solid fraction. Friction losses in the elbows are about 1.55–2.16 times that in the horizontal straight pipe, which is about 2.7–10.0 kPa·m-1. The pipe-loop test data can be used to analyse the rheological priorities of cemented unclassified tailings slurry. Based on the Buckingham rheological equation, an empirical formula for friction losses was established and applied to a pipe with the optimal diameter of DN 150 mm. It can be concluded that the full-scale pipe-loop test is an effective way to investigate friction losses and the economics of design pipeline transportation.

West orebody is now the main production zone of Chambishi Copper Mine. Upward drift stoping is performed to meet the annual ore production of more than 1 Mt. Cemented classified tailings backfill was originally employed, which then proved to be both economically and operationally impractical due to high cement cost, low metal recovery, severe backfill tailings shortage, etc. As an alternative, the current paste backfill system with low cement addition was suggested after a comprehensive study and investigation. Construction work of the paste backfill system started in 2012. The system was put into production at the beginning of 2014 after commissioning. During commissioning, the backfill system reached a capacity of 60 m3/h with the paste concentration of 68 to 70%, and the friction loss of the pipeline transport was 4-6 MPa/km. To meet the backfill strength, the cement to tailings ratio for primary stopes was 1:12, and 1:30 for secondary stopes. As a result, the composite cost for backfill was only USD 15 to 20 /m3, while ore recovery increased by 35% and mining to cutting ratio dropped by 80 m3/kt. Since commissioning investigations indicate that this paste backfill system will be capable of prolonging west orebody’s service by about 10 years, and will bring about enormous economic returns. This paper presents the case study of the highly automated system and its commissioning performance, with emphasis on key processes including unclassified tailings thickening, two-stage slurry mixing, paste pumping, and underground backfill.

The development of paste technology has been similar around the world, from non-ferrous and gold mines to other kinds of metal mines. In recent years, paste technology has rapidly spread to iron mines. Iron ore deposits in China are usually irregular, fractural and of low grade. Therefore, the managers have to use large scale mining to reduce the mining cost per unit; large scale backfill systems are required for the safe operation of large scale extraction. Consequently, backfill systems with a large flow capacity are used in iron mines. The Lilou Iron Mine backfill capacity has reached 160-180m3/h with an annual mining production of 7.5 m t ore, the filling cost of which is CNY 18-30 per tonne of extracted ore.

The bacteria column leaching experiment of low grade sulphide ore was conducted and the ore granular media were scanned by X-ray computerised tomography scanner before and after leaching. Based on the image processing operation, the spatial distribution of the porosity, and the change of pore size distribution and connectivity before and after leaching were investigated. In addition, the mechanism of pore evolution during leaching was also analysed. The results indicate that the porosity, pore size and pore connectivity of the ore granular media during leaching all have spatial and temporal variability. After leaching, the porosity distribution along the column became more inhomogeneous and assumes a decreasing trend from top to bottom, especially the bottom zone, with porosity decreasing greatly. The amount of larger pores increased at the top and middle zones after leaching while decreased at bottom zone. The connectivity of the top and middle zone was improved but deteriorated at the bottom zone. The main mechanisms for pore evolution are the subsidence of the entire granular ore body and the transportation and accumulation of the fine particles, chemical precipitates and colloidal substance at local areas.

Dexing Copper Deposit, located in Jiangxi province, China, is one of the largest porphyry copper deposits in the world, the copper content of which exceeds eight million tonnes. Fine hundred million tonnes of waste rock with grades between 0.1 and 0.3 will be produced during open pit mining of Dexing. The amount of copper metal is 1.2 million tonnes. In order to extract copper metal from those secondary resources and resolve the environmental problems caused by acidic water and heavy metals released from the waste rock dump, a dump bioleaching-solvent extraction-electrowinning plant was designed based on a series of experimental investigations. Presently, there are a number of challenges faced by this plant, such as low recovery efficiency, low Cu2+ concentration and limited production. The investigation shows that the low- grade of the dump, refractoriness of chalcopyrite, small sprinkling area, leakage of pad, small bacteria population, low dump permeability are the main factors that contribute to the challenges. Several measures were exercised by the plant, such as separating ores from rocks, stripping and loosening the surface layer of dump, loosening the entire dump by use of explosives. Besides those challenges, stability of the high and steep slope of the dump is a hidden danger to which much attention is not paid. The height of the dump exceeds 70 m, and the inclination of the slope is 55°. The failure of dump could result in a dangerous disaster. Mechanical properties of the waste rock before and after leaching were investigated. The result shows that the normal stress, shear strength and cohesion decreased sharply during the leaching process.