Recycled metals, separation

Plastic and Metals Recycling Electrostatic separation has been inereasinglv applied to recover nonFerroiis metals From industrial plasties (telephone and eornrniinieation scrap). It also is an important step in the reeveling oF beverage bottles to reject anv remaining nonFerroiis metals. Both oF these reeveling applications make use oF roll-type ion-bornbardrnent separators (Fig, 19-61/ ),... 

The main difference between these two methods is that in MBT method, mixed waste is separated into organic, recyclable, metal, inert, and high-caloric... 

Description of the process. The simplified process flow diagram is shown in Figure 16.12. The shredder waste (ASR, plastic and electronic waste as well as MSW) is fed in an IRFB, which operates in a reducing atmosphere and at temperatures as low as 500-600°C, allowing easy control of the process. The IRFB reactor separates the combustible portion and the dust from the inert and metallic particles of the fed waste the obtained mixture of metallic and inert particles is sent to a mechanical metal separation while fuel gas and carbonaceous particles are burnt in a cyclonic combustion chamber for energy production and fine ash vitrification. Metals such as aluminium, copper and iron can be recycled as valuable products from the bottom off-stream of the IRFB as they are neither oxidized nor sintered with... 

Lead is the most recycled metal, for several reasons It is too toxic to go to landfills the major use is in automobile batteries, which have a predictable life span and used batteries are collected at legally designated locations in most states. Iron and steel are second in percentage recycled, most of which is recycled within the industry rather than from consumer products. Iron and steel are used in vastly greater quantities than all other metals combined, resulting in a huge pool of scrap to be dealt with. Not recovering it would be a financial as well as an environmental burden. Also, all steel is potentially recyclable without separation of pure metals from the mixture. 

Recycling metals such as aluminum, iron, and lead has been occurring for years (Section 8.6). However, programs for recycling plastics developed much more slowly because of the costs associated with separating different types of plastics and producing usable recycled products from the used plastics. 

The US EPA provides a website for guidelines for generating electricity from MSW (EPA 2010). The MSW is unloaded at the waste-to-energy facility. Metals, glass, and other recyclables are separated out. The remaining burnable waste is fed into a combustion chamber and burned. The released heat produces steam that turns a steam turbine and generates electricity. 

Catalyst may be packed in a fixed bed within the reactor. Uniformly small particles may also be supported by the upward velocity of the reactant stream (gas or liquid), in which case it is called a fluidized bed. Solid catalyst may also be dissolved or suspended in a liquid reaction media, then separated from the products and recycled. Metal catalysts may be made into screens or other shapes across which the reactants flow. It should be remembered, however, that the reaction takes place on the surface of the catalyst if heat is evolved, cooling should be applied there, or the catalyst could be destroyed or deactivated. Most catalysts also become deactivated due to fouling of the surface with by-products and contamination by impurities in the feed stock, called poisons. The... 

It is not always easy to recycle metals. They have to be collected and sorted and then transported to the recycling plant. This takes energy and money. It maybe difficult to separate individual metals. For example tin cans are made from steel coated with tin. The two metals have to be separated before they can be used again. Two metals that can be recycled easily are copper and aluminium. 

Heavy metals often can be removed effectively by chemical precipitation in the form of carbonates, hydroxides, or sulfides. Sodium carbonate, sodium bisulfite, sodium hydroxide, and calcium oxide are all used as precipitation agents. The solids precipitate as a floe containing a large amount of water in the structure. The precipitated solids need to be separated by thickening or filtration and recycled if possible. If recycling is not possible, then the solids are usually disposed of to a landfill. 

Reverse osmosis is a high-pressure membrane separation process (20 to 100 bar) which can be used to reject dissolved inorganic salt or heavy metals. The concentrated waste material produced by membrane process should be recycled if possible but might require further treatment or disposal. 

Each vehicle generates 500—800 pounds of residue. The aimual U.S. total is about 3.5 million tons or about 1.3% of the municipal soHd waste generated aimuaHy (3). The mixture is too complex to separate and recycle. Depending on the amount of glass, water, metal, and dirt present, the residue... 

Catalyst recovery is a major operational problem because rhodium is a cosdy noble metal and every trace must be recovered for an economic process. Several methods have been patented (44—46). The catalyst is often reactivated by heating in the presence of an alcohol. In another technique, water is added to the homogeneous catalyst solution so that the rhodium compounds precipitate. Another way to separate rhodium involves a two-phase Hquid such as the immiscible mixture of octane or cyclohexane and aliphatic alcohols having 4—8 carbon atoms. In a typical instance, the carbonylation reactor is operated so the desired products and other low boiling materials are flash-distilled. The reacting mixture itself may be boiled, or a sidestream can be distilled, returning the heavy ends to the reactor. In either case, the heavier materials tend to accumulate. A part of these materials is separated, then concentrated to leave only the heaviest residues, and treated with the immiscible Hquid pair. The rhodium precipitates and is taken up in anhydride for recycling. 

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