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重介质选矿一般只适用于大于1毫米而且孔隙变低的矿粒。多孔性矿石之所以不能获得满意的结果是由于:(1)在常规比重分析与工业分选过程之间有甚大的差异;(2)矿物的变化的孔隙度对表面性质的影响;(3)比表面大而且吸附了一层水膜的颗粒的絮凝或凝聚,这种水膜的表面张力大于所用的分选液的表面张力。比重低于重液的水或多或少会被吸收一些,因此就难于保持恒定的密度和粘度特性。不同视比重的矿物颗粒在浸于有机重液中时导致了絮凝和凝聚,这就使按比重分离无效而且丧失意义。絮凝也会出现在重介质悬浮液中,矿物颗粒和硅铁两者都能生成絮凝体。絮凝体能较快地沉降下来,因而就破坏了悬浮液的稳定性和均匀性。而且硅铁颗粒能形成一种包含或不包含矿石颗粒在内的稳定粒团,其行为就象单独的颗粒一样。因此,就出现比重反常而使分选结果不一致,还增加介质的损耗。在用有机重液的重力分选中,矿物颗粒所吸收的水,被表面张力低的重液所排挤,接着,重液即或多或少地穿透到矿物颗粒里面去,这样就改变了矿物颗粒的视比重,而使分选结果不一致,而且过多地消耗重液。用表面活性剂的水溶液来代替水以消除这些弊病,可以使实验室的重液分选试验与工业分选一致。表面活性剂溶液的表面张力必须低于有机重液(多为溴仿或四溴乙烷)的表面张力。这样,重液分选实际上就可以用于小到0.1毫米的粒度。重液的损耗就变少,因为疏液薄膜封闭了矿物的孔隙而阻止有机重液的吸收。这层薄液的表面张力低于重液的表面张力,因此它不能被重液从矿物表面上置换下来。
Heavy media beneficiation is generally only applicable to ore particles larger than 1 mm and with lower porosity. The reason that porous minerals can not be satisfactorily achieved is due to: (1) a significant difference between conventional gravimetric analysis and industrial separation processes; (2) the effect of varying porosity of minerals on the surface properties; (3) The flocculation or coalescence of particles larger in surface area and adsorbed by a film of water, whose surface tension is greater than the surface tension of the used separation fluid. Water with a lower specific gravity than the heavy liquor is absorbed more or less, making it difficult to maintain constant density and viscosity characteristics. Mineral particles of different apparent specific gravity lead to flocculation and coagulation when immersed in an organic heavy liquor, which renders the separation by weight ineffective and meaningless. Flocculation also occurs in heavy media suspensions, where both mineral particles and ferrosilicon generate flocs. The flocs settle down more rapidly, thus destroying the stability and uniformity of the suspension. Moreover, ferrosilicon particles form a stable mass of particles, with or without ore particles, behaving like individual particles. As a result, there is an abnormal proportion of sorting results appear inconsistent, but also increase the loss of the medium. In gravitation sorting with organic heavy fluids, the water absorbed by the mineral particles is squeezed out by the heavy fluid of low surface tension, and then the heavy fluid penetrates more or less into the mineral particles, thus changing the mineral Depending on the specific gravity of the particles, the sorting results are inconsistent, and excessive consumption of heavy fluid. Replacing water with an aqueous surfactant solution to eliminate these drawbacks allows laboratories to reconstitute heavy liquor sorting tests in line with industrial sorting. Surfactant solution surface tension must be lower than the organic heavy liquid (mostly bromoform or tetrabromoethane) surface tension. In this way, heavy liquor sorting can be practically used for particle sizes as small as 0.1 mm. Heavy fluid loss will be less, because the lyophobic film closed the pores of minerals and prevent the absorption of organic heavy liquid. The surface tension of this thin liquid is lower than the surface tension of heavy fluid so it can not be displaced from the mineral surface by the heavy fluid.