Reclaimed sheet

As indicated in Chapter 1, global lead consumption from secondary sources approached four million tonnes per year in 2005, or 60 per cent of total world consumption. Around 20 per cent of world consumption is for uses where recycling is difficult, such as for plastics stabilisers, for TV tube glass, for shot and ammunition. Of the remainder, ten per cent is used for rolled or extruded alloys and cable sheathing, which have long-term applications, and 70 per cent is used for batteries. Recyclable lead therefore is predominantly from used automotive batteries, with some from reclaimed sheet, cable sheathing and other metallic scrap. In addition there are various residues, drosses and flue dusts containing lead. 

In addition to the two reviews that are mentioned at the beginning of this section, a number of other relatively recent reviews of the processes and methods that have been developed and evaluated for the devulcanisation of waste rubber are available. For example, Majumdar published an overview in 2009 in the Chemical Weekly journal [4], which covered the challenges that face workers in this field and covered the main types of systems that have been developed (i.e., chemical, microwave, ultrasonic and so on). This article also covered the production and use of rubber crumb from waste rubber. In another article [5], Majumdar reviews the three main sources of reclaimed rubber that are available in the marketplace (rubber crumb, rubber powder and chemically digested reclaimed sheet) and describes their properties and uses. 

Fig. 8-52 The addition of an extruded single plastic clamping strip at each side of a coextruded sheet permits scrap reclaim of the trim waste.

The percentage sulphur (determined in the un-vulcanized reclaim) and the available rubber hydrocarbon are taken into consideration while evolving the compound formulation. It should be noted that reclaimed rubber is not all rubber. In arriving at the total rubber content in the rubber formulation containing reclaim, allowance must be made for its rubber content. For example in the following blend of smoked sheet and whole tyre reclaim, the total rubber content is to be considered as 100 parts instead of 125 parts as below and the proportion of other ingredients should be worked out accordingly on "parts per hundred rubber" (phr) basis. 

Another 3x10 tonnes of lead are produced from secondary sources each year, by recycling scrap lead products such as sheet, pipe and batteries. Today, in the western world, more lead is produced by recycling than by mining. More than 50% of the lead consumed in the US is in the form of batteries, and of this about 90% is reclaimed. At present, battery scrap is converted to impure lead or lead alloys by pyro-metallurgical processes employing blast, reverberatory, or rotary furnaces. The overall recovery of the metallic components of scrap in plants having both reverberatory and blast furnaces is > 95%. 

In another study, the ground reclaim rubber was blended with stirene-butadiene rubber and cured under pressure at 160°C. The cured sheets were silica-reinforced by soaking in tetraethyl ortho silicate, then in an aqueous solution of n-butyl amine catalyst, followed by heat treatment at 50°C. The tensile properties of the blends containing conventionally incorporated silica, with no coupling agent, were superior to those containing silica incorporated by the sol-gel reaction [21]. 

Certain polymers are not readily amenable to this simple sequence and chemical processes are being increasingly adopted which reprocess the material to an earlier stage of manufacture. Transparent sheet of polymethymethacrylate (PMMA) is one instance where, to retain the transparency and colour, reclaimers must resort to distillation to recover... 

Electrolysis is used for extracting copper from poor ores, and for reclaiming scrap copper. The copper is brought into solution as copper (II) sulphate, and this is electrolysed with a cathode of sheet copper and a lead-alloy anode. Oxygen is liberated at the anode and sulphuric acid accumulates in the electrolyte. When the electrolyte is exhausted, the sulphuric acid is used to bring more copper into solution. 

Heater or pan process A steam autoclave is used at 100-300 psi for an extended time with ground rubber mixed with reclaiming agents, such as 20% ammonium persulfate solution. After the process, the product is mixed with an aromatic oil and formed into sheets. 

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