Mineral Processing Flowsheets

Separation processes, as could be seen from Figure 2.1, position themselves at the back end of the sequence in operations in the mineral processing flowsheet. The front-end operations has been found virtually to terminate with the liberation or the size-reduction processes involving crushing and grinding. It is important to limit the amount of size reduction to that at which adequate liberation is accomplished. The term adequacy is related to the cost involved in comminution and to performance of the concentration methods that follows. The concentration is obtained by separation processes which rely on differences in the properties of the particles, the physical and physico-chemical characteristics of minerals. In this context, it will only be relevant to refer to Table 2.5 which presents a summary of the processes along with the properties of the minerals that are exploited. 

This section on flowsheets basically aims to provide some illustrative examples of the use of the various mineral processing unit operations that have been described. A general flowsheet involving almost all the unit operations pertinent to mineral processing is shown in Figure 2.32. The others refer specifically to beach sands, lead-zinc concentration, molybdenum, and the rare earths. 

Figure 2.35 (A) Flowsheet for heavy mineral processing in Thailand. (B) Flowsheet for processing bastnasite from mountain pass, California.

Hartge EU, Pogodda M, Reimers C, Schwier D, Gruhn C, Werther J SolidSim—a tool for the flowsheet simulation of solids processes, AT Miner Process 47 42—51, 2006. 

Molybdenum is not found naturally in its elemental form. It is obtained primarily from the mineral molybdenite (MoS2), which contains an average 59.9% of molybdenum. It is the only source of molybdenum which accounts for most of the world s molybdenum supply. Processing flowsheet of molybdenum from this commercial source into principal commercial forms is illustrative of the wide and diverse applications of molybdenum and its chemicals (Figure 1.19). 

The electrostatic separation method is the exclusive choice in some specific situations, for example in the cases of rutile and ilmenite deposits. These deposits generally contain minerals of similar specific gravities and similar surface properties so that processes such as flotation are unsuitable for concentration. The major application of electrostatic separation is in the processing of beach sands and alluvial deposits containing titanium minerals. Almost all the beach sand plants in the world use electrostatic separation to separate rutile and ilmenite from zircon and monazite. In this context the flowsheet given later (see Figure 2.35 A) may be referred to. Electrostatic separation is also used with regard to a number of other minerals. Some reported commercial separations include those of cassiterite from scheelite, wolframite from quartz, cassiterite from columbite, feldspar from quartz and mica, and diamond from heavy associated minerals. Electrostatic separation is also used in industrial waste recovery. 

The alkali process uses sodium hydroxide and is well known as Bayer s process. It involves relatively simple inorganic and physical chemistry and the entire flowsheet can be divided into caustic digestion, clarification, precipitation and calcination. Although mineral assemblage in bauxites is extensive, processing conditions are primarily influenced by the relative proportions of alumina minerals (gibbsite and boehmite), the iron minerals (goethite and hematite), and the silica minerals (quartz and clays-usually as kaolinite). 

The present description pertaining to copper refers to solvent extraction of copper at the Bluebird Mine, Miami. When the plant became operational in the first quarter of 1968 it used L1X 64, but L1X 64N was introduced in to its operation from late 1968. The ore consists of the oxidized minerals, chrysocolla and lesser amounts of azurite and malachite. A heap leaching process is adopted for this copper resource. Heap-leached copper solution is subjected to solvent extraction operation, the extractant being a solution of 7-8% L1X 64N incorporated in kerosene diluent. The extraction process flowsheet is shown in Figure 5.20. The extraction equilibrium diagram portrayed in Figure 5.21 (A) shows the condi-... 

Selection of a flotation technique for gold preconcentration depends very much on the ore mineralogy, gangue composition and gold particle size. There is no universal method for flotation of the gold-bearing minerals, and the process is tailored to the ore characteristics. A specific reagent scheme and flowsheet are required for each ore. 

Alkaline breakdown of monazite. —The flowsheet for the process is given in Fig. 5. For this process it is necessary to remove calcium from the monazite by boiling the mineral with nitric or hydrochloric acid. It has long been known that monazite can be attacked by alkali. Rohden and Peltier [149] have shown the practical applicability of the alkali process for monazite decomposition. The optimum conditions necessary for alkaline decomposition of monazite have been extensively studied by Kaplan and his coworkers [150—153]. 

Ores containing essentially pure gibbsite may be digested at temperatures of ]50 C while boehmilic ores require temperatures in rbe range of 230-250 C. These temperatures reflect the differences in the solubilities of the various hydrated aluminum minerals, Figure 9.2-4 illustrates a typical Bayer process flowsheet. 

Qualitative flowsheets are given for the extraction and purification of all the rare metals discussed in earlier chapters. As far as possible the examples chosen are typical of current practice or of recently proposed processes. Each flowsheet presented begins with a mineral ore and ends with a pure metal, whereas in practice the various component operations are sometimes divided between two or more plants e.g. in the case of uranium, it is convenient to produce a concentrate containing about 70 per cent of the element near the minefield and to ship this to various refineries many thousands of miles away. Metal production may take place at the refinery, or in yet a third factory in association with subsequent metallurgical stages. 

A continuous pilot plant test of the flowsheet (Figure 6) was established at SGS Minerals. The first four steps in the process, PLATSOL , PGM cementation, copper concentrate enrichment and copper precipitation were included in the continuous run. The copper depleted solution from copper precipitation was collected and a series of batch tests were used to complete the remaining flowsheet steps. The step by step results of the testing are summarized below. 

---