Concentration.doc

ConcentrationThe object of mineral processing, regardless of the methods used, is always the same, i.e. to separate the minerals into two or more products with the values in the concentrates, the gangue in the tailings, and the “locked” particles in the middlings. Such separations are, of course, never perfect, so that much of the middlings produced are, in fact, misplaced particles, i.e. those particles which ideally should have reported to the concentrate or the tailings. This is often particularly serious when treating ultra-fine particles, where the efficiency of separation is usually low. In such cases, fine liberated valuable mineral particles often report in the middlings and tailings. The technology for treating fine-sized minerals is, as yet, poorly developed, and, in some cases, very large amounts of fines are discarded. For instance, it is common practice to remove material less than 10 micron in size from tin concentrator feeds and direct this material to the tailings, and, in the early 1970s, 50% of the tin mined in Bolivia, 30% of the phosphate mined in Florida, and 20% of the worlds tungsten were lost as fines. Significant amounts of copper, uranium, fluorspar, bauxite, zinc, and iron were also similarly lost. The recovery, in the case of the concentration of a metallic ore, is the percentage of the total metal contained in the ore that is recovered in the concentrate; a recovery of 90% means that 90 % of the metal in the ore is recovered in the concentrate and 10 % is lost in the tailings. It is possible to speak of the recovery of metal in tailings, middlings, and other products, but normally the term refers to the amount of metal recovered in the concentratesthe valuable products. Essentially the purpose of calculating recovery is to determine the distribution of the metal in the feed (or heads) among the various products of the mineral-dressing operations. The recovery, when dealing with non-metallic ores, refers to the percentage of the total mineral contained in the ore that is recovered into the concentrate, i.e. recovery is usually expressed in terms of the valuable end product. The ratio of concentration is the ratio of the weight of the feed to the weight of the concentrate. It is a measure of the efficiency of the concentration process, and it is closely related to the grade or assay of the concentrate; the value of the ratio of concentration will generally increase with the grade of concentrate. The grade, or assay, usually refers to the content of the marketable end product in the material. Thus in metallic ores, the per cent metal is often quoted, although in the case of very low-grade ors, such as gold, the metal content may be expressed as parts per million (ppm). Some metals are sold in oxide form, and hence the grade may he quoted in terms of the marketable oxide content, e.g.%WO 3, %U3O8, etc. In non-metallic operations, grade usually refers to the mineral content, e.g. %CaF2 in fluorite ores; diamond ores are usually graded in carats per 100 tonnes (t), where 1 carat is 0.2 g. Coal is graded according to its ash content, i.e. the amount of incombustible mineral present within the coal; most of the coal produced in Britain is consumed in power stations, which require a feed with an ash content of between 15 and 20%. The enrichment ratio is the ratio of the grade of the concentrate to the grade of the heads, and again is related to the efficiency of the process. Ratio of concentration and recovery are essentially independent of each other, and in order to evaluate a given operation it is necessary to know both. For example, it is possible to obtain a very high grade of concentrate and ratio of concentration by simply picking a few lumps of pure galena from a lead ore, but the recovery would be very low. On the other hand, a concentrating process might show a recovery of 99% of the metal, but it might also put 60% of the gangue minerals in the concentrate. It is, of course, possible to obtain 100 % recovery by not concentrating the ore at all. There is an approximately inverse relationship between recovery and grade of concentrate in all concentrating processes. If an attempt is made to attain a very high-grade concentrate, the tailings assays are higher and the recovery is low. If a high recovery of metal is aimed for, there will be more gangue in the concentrate and the grade of concentrate and ratio of concentration will both decrease. There is always, therefore, an economic optimum in the combination of grade and recovery. It is impossible to give figures for representative values of recoveries and ratios of concentration. The cost of milling, value of the metal, use for which the concentrate is intended and the nature of the ore, must all be considered; and each ore is a separate problem. A concentration ratio of 2 to 1 might be satisfactory for certain high-grade non-metallic ores. But a ratio of 50 to 1 might be considered too low for a low-grade copper ore; ratios of concentration of several million to one are common with diamond ores. The aim of milling operations is to maintain the values of ratio of concentration and recovery as high as possible, all factors being considered.我做的翻译。Concentration精矿虽然所使用的方法不同，但矿物加工的目的，都是一样的，即把矿物根据所含价值的不同，以及尾矿中所含矿分的不同，以及中煤含量的不同等因素，分成两种或更多的产品。当然,这样的分离并不完美,所以,很多中间产品被错放了位置。例如那些理想状态下，本应该是精矿或者尾矿的矿石被放错了位置。通常当对待超细颗粒时，这种分离效率低的情况尤为严重。在这种情况下,再细分解宝贵的矿物颗粒经常会在中矿和尾矿中。处理精矿的技术仍然很不发达，而且在某些情况下，很多的精矿被丢弃掉了。例如,按照惯例，从锡矿精矿材料中，移除大小小于10微米的原料，然后直接将此原料放在尾矿中，在20世纪70年代早期，保加利亚50%的锡矿、弗罗里达30%的磷矿、世界上20%的钨矿在开采中被这样消失了。大量的铜、铀、萤石、铝土矿、锌和铁也同样失去了。金属精矿矿石的回收,是在矿石中总金属含量; 90%的回收率意味着90%的金属在矿石中被回收在精矿中，10%的金属消失在尾矿中。我们可以说金属在尾矿，中矿和其他产品中可以被回收，但是通常，这种术语指的是在精矿-宝贵的产品中回收的量。基本上，计算回收率的目的是确定金属在原矿中的分步，在选矿操作中得到的各种产品。在处理非金属矿石时,回收率指的是矿物在回收到精矿矿石中的百分比，例如，回收产品通常被表述称有价值的终端产品。精矿的比率通常指原料的重量比精矿的重量。 这是一个高效的精矿过程的测量办法，而且他与精矿的等级和含量有关；精矿的价值率将随着精矿等级的增加而增加。 等级或者含量通常指原矿中有价值的终端产品。因此在金属矿石中，尽管在金矿这种很低等级的矿中，金属含量可能是百万分之一，金属百分比也经常被应用。一些金属以氧化物形式出售,因此他的等级可能以有价值的氧化物含量被应用。例如.%WO 3, %U3O8等。在非金属开采中，等级通常