Tailings separation processes

Gangue. Undesired minerals associated with ore, mostly nonmetaUic. Gangue represents the portion of ore rejected as tailings in a separating process. It is usually valueless, but may have some secondary commercial use. 

The Separation Stage. A fundamental quantity, a, exists in all stochastic separation processes, and is an index of the steady-state separation that can be attained in an element of the process equipment. The numerical value of a is developed for each process under consideration in the subsequent sections. The separation stage, which in a continuous separation process is called the transfer unit or equivalent theoretical plate, may be considered as a device separating a feed stream, or streams, into two product streams, often called heads and tails, or product and waste, such that the concentrations of the components in the two effluent streams are related by the quantity, d. For the case of the separation of a binary mixture this relationship is... 

Likewise, fly ash from power plant combustors often contains small amounts of metals or their oxides, which require costly disposal in the ever-shrinking number of approved hazardous waste landfills. Thus, there are economic incentives to recover the metal values as well as to reduce the costs of ultimate disposal. Here, too, the metal content is low, and research is needed to develop economical separation processes. In principle, advances in this area could be translated into recovery of metal values from mine tailings. 

A common feature of all separation processes is that they are imperfect - some of the materials of no value contaminate the concentrate to some extent, and some of the minerals of value are always present in the tailings in small amounts. 

Cellulose is itself polar in nature and can cause some adsorption, which may result in the tailing of zones. However, this adsorptive effect may contribute to the separation process in some instances and the use of a polar mobile phase can enhance this effect further, e.g. the separation of amino acids using an aqueous solution of ammonia as the mobile phase. The combination of partition and adsorption generally influences separations on cellulose thin-layer plates, which have superseded paper chromatography in most instances and offer increased speed and resolution. 

It has been found that from a homogeneous solution the oxalate of samarium is preferentially precipitated over oxalates of other rare earths and yttrium falls behind all of them. Thus, in a separation process Sm is concentrated to a greater extent at the head section and Y at the tail section [45]. 

The tailings from the various flotation stages of an industrial separation process can be combined and hydraulically transported by pipeline ([90,606], see also Section 10.2). Sometimes the tailings pipelines are dose to the separation plants, and therefore are of modest length, but it is not uncommon for such pipelines to extend for several tens of kilometres to a settling basin. 

In many surface-separation processes, there will occur three distinct phases or process streams a product stream (either oil or water), a waste (tailings) stream, and an interface or rag layer emulsion stream, which may contain emulsified oil and/ or water. The interface emulsion can be the most troublesome, in terms of process operation, and the most complex and intractable, in terms of treatment. Mikula shows (Figure 1 in Ref. [66]) a photomicrograph of a quite stable interface emulsion (rag-layer emulsion) in which one can clearly observe the simultaneous occurrences of both O/W and W/O emulsions in different regions of the same sample. 

Tailing. A condition where the front of the peak is steeper than the rear relative to the baseline. This condition results from nonideal equilibria in the separation process. 

In agitated tank leaching systems, finely ground ore must be mixed with the lixiviant until the reaction is complete. Liquid/solid separation processes are used to recover the solution and prepare the waste for disposal in a tailing impoundment. Unlike percolation leaching operations, these operations require a large impoundment area to not only handle the solids, but also to neutralize the chemistry and pH of the solutions used to extract the metal value. 

Process design the report gives several examples of products that reduce environmental impact. It also identifies that electricity is the principal component of the air separation process, and that we constantly strive to improve the energy efficiency of our plants . Even so a no score has been awarded since only one example of a process improvement is given (changing a cleaning system to reduce ozone emissions), while at the same time the report includes a number of examples where tail-end treatment has been used to reduce emissions. 

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