| Ore bodies in Jinchuan Nickel Mine consist of large-scale sulfide copper and nickel mineralization which are extremely difficult to extract due to their deep buried depths, thick ore bodies, broken surrounding rock bodies and high geostress. Historically based on practical production experience and large amount of technological studies, a conservative downwards layered cut and fill mining method with low productivity and high mining cost was adopted. At present, the main filling material is rod-mill-sand aggregate and cementing material which is pipeline transported with high density and high sand-cement ratios. Te most expensive filling cost has put lots of financial pressure onto the mining company and need to be cut urgently.This paper based on Jinchuan Company major scientific research project "Research on development for new filling cementing material and utilization of solid waste" and science and technology key project "Mining support theory and key technology at Jinchuan super large complex mine". Aimed to make use of the large amount of solid wastes around the Mine, by using phosphogypsum from Wengfu Chemical Factory, and granulated slag from Jinchang Iron Mill, a new kind of early strength cementing material was developed and its pipeline transportation characteristics was studied. Those works have laid the theoretical foundation on the improvement of cut-fill mining cost and better utilization of solid waste around Jinchuan Mine.Main works and conclusions are as the followings:(1) The original designed strength of filling body was:1.5MPa,2.5MPa,5.0MPa for curing days3d,7d,28d respectively. As the mining depth is more than1,000meters below surface ground, to ensure mining safety and mining efficiency, the designed compressive strength of filling body needs to be verified to adapt to the surrounding rock geostress. By collecting and analyzing measured geostress data, using BP neutral network software, a geostress prediction model was set up to make analysis of regression and prediction the geostress distribution around the underground mining areas. This work provides basic geostress reference for the filling body strength in desired area. Based on the strength calculation and the multiple filling body strength requirements, it was found out that the former criterion on filling body strength is still suitable for the deep underground backfilled areas.(2) Originally, to accomplish the required early filling body strength, the filling slurry is gravitational flow and must has high cement and sand ratio1:4and high density up to77%-79%. By doing this, not only the backfilling cost is high (RMB165.00/m3), but also the pipeline transportation techniques must meet higher standard to cope with the high density gravitational slurry flow. Therefore, further research work was done to develop early strength material from phosphogypsum and granulated slag.Firstly the physicochemical properties of the phosphogypsum and granulated slag was analyzed, then different booster recipe was orthogonally tested. By using range analysis, BP network module and regression analysis, the relationship and varying pattern was drawn out between cementing material characteristics and the amount of booster additive. It was found that for phosphogypsum-based booster the optimum recipe is quick lime5%, phosphogypsum25%, sodium hydroxide2%, sodium sulfate2.5%, granulated slag65.5%. Verification test was performed to determine the ratio between optimized cementing material and sand. The best slurry is new cementing material and sand ratio1:4and density78%, the corresponded compressive strength is1.85MPa,3.06MPa,8.69MPa after3d,7d,28d curing days respectively. The filling body strengths meet Jinchuang Mine’s requirements(R3≥1.5MPa, R7≥2.5MPa, R28≥5MPa). The new cementing material costs only66%price of the regular cement R325.(3) To further promote the material behavior of the phosphogypsum-slag cementing material, SEM electronic microscope and XRD diffraction were used to find out hydration mechanism and early solidation formation process. It was found out that the fine particles in the slag start hydration reaction when boosted by phosphogypsum. Main hydration products are tobermorite (Calclium Silicate Hydrate) and ettringite(AFt). Phosphogypsum speeds up the reaction process of producing CSH and AFt, then the water in slurry is absorbed quickly and then filling body becomes harden and densified. Tobermorite acts as filling and gluing material while ettringite acts as cross link and supporting. The phosphogypsum takes part in hydration reaction and becomes less and less while CSH and AFt becomes more and more.(4) To apply this new phosphogypsum-slag cementing material into Jinchuan Mine, further pipeline transportation characteristics was also tested with high density slurry. Slurry flow parameters were recorded and analyzed. Test results showed the rheological properties of the new cementing material has no essential difference compared with that of traditional cement mixed slurry and can meet the Mine’s requirement(Denseness≥9cm, Collapsibility≥20cm, Layered thickness≤2.0cm). Study also showed if cement and sand ratio equals1:4while slurry density78%, the new cementing material slurry when flowing in pipeline is Bingham Body, which shows homogeneous and laminar fluid.By applying tested parameters into F1UENT Simulating System to test the resistance force when the slurry is transported by pipeline. Varying patterns of slurry fluid speed, stream core, pressure, frictional resistance was simulated and analyzed with different pipeline sizes, bending angles, transporting distances. Study shows that as a substitute for traditional cement, phosphogypsum-slag-based early strength cementing material can be used in high density gravitational slurry flow system in deep underground backfill operation with safety, efficiency, green and economy. |
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