Spent Material

Although more often associated with household and commercial waste, recycling has proven to be very successhil in the industrial arena. Industrial recycling is the recovery for reuse or sale of materials from what otherwise would be wastes destined for disposal (5). Typically, the reclaimable materials employed in industrial recycling may consist of obsolete products, spent materials, industrial by-products or residues, or pollution control products. The recycling of many of these products is so well estabHshed that under standard commercial practices such materials are destined only for recovery, not for disposal. 

Spent materials are materials that have been used and can no longer serve the purpose for which they were produced without processing. For example, a solvent used to degrease metal parts will... 

Byproducts are materials that are not one of the intended products of a production process. An example is the sediment remaining at the bottom of a distillation column. Byproduct is a catch-all term and includes most wastes that are not spent materials or sludges. Listed byproducts are solid wastes when reclaimed used in a manner constituting disposal burned for energy recovery, used to produce a fuel, or contained in fuels or accumulated speculatively. On the other hand, characteristic byproducts are not solid wastes when reclaimed, unless they are used in a manner constituting disposal burned for energy recovery, used to produce a fuel, or contained in fuels or accumulated speculatively (Table 13.1). 

Closed-loop recycling. To further promote waste reduction and recycling, spent materials that are reclaimed and returned to the original process in an enclosed system of pipes and tanks are excluded from the definition of solid waste, provided that the following conditions are met ... 

Mineral processing spent materials. Mineral processing generates spent materials that may exhibit hazardous waste characteristics. Common industry practice is to recycle these mineral processing wastes back into the processing operations to recover mineral value. U.S. EPA created a conditional exclusion from the definition of solid waste for these spent materials when recycled in the mineral processing industry, provided the materials are stored in certain types of units and are not accumulated speculatively. 

Interaction is exothermic, and if air is present, incandescence may occur with freshly prepared granular material. Admixture with oxygen causes a violent explosion [1], Soda-lime, used to absorb hydrogen sulfide, will subsequently react with atmospheric oxygen and especially carbon dioxide (from the solid coolant) with a sufficient exotherm in contact with moist paper wipes (in a laboratory waste bin) to cause ignition [2], Spent material should be saturated with water before separate disposal. Mixture analogous to soda-lime, such as barium hydroxide with potassium or sodium hydroxides, also behave similarly [1],... 

MANAGEMENT OF SPENT MATERIALS 4.3.1 Activated carbon regeneration and reactivation... 

For example, if the carbon has been used for the removal of PCBs, dioxins, or heavy metals, and generally in the case of powdered activated carbons, the disposal of the spent material is the most appropriate method. 

Spent ion-exchange and adsorption materials represent a special type of waste, and pose unique problems in the selection of their treatment options. With the evolution of environmental legislation, it is now required that spent materials meet specific quality requirements prior to disposal. In the selection of the treatment method for spent materials, their physical and chemical characteristics must be considered. Basically, there are two main treatment methods destruction and immobilization. In several occasions, depending on the nature of the spent material, a pretreatment step is required. 

Dewatering-. Dewatering the spent materials prior to immobilization improves the overall volume reduction and the compatibility of the waste with the immobilization process. Dewatering is generally accomplished by pressure, vacuum filtration, or centrifugation. 

Crushing and grinding Crashing and grinding techniques are used basically for size reduction of spent materials, which results in a more homogeneous waste for immobilization, allows the easier removal of nonspecific materials, and facilitates the further destruction of the material by thermal, chemical, or biological methods. 

The main goal of destructive methods is to conveniently alter the physicochemical characteristics of the spent material before its final disposal. These processes can be classified as thermal and nonthermal processes. 

Bitumen processes can be held either as batch or as continuous operations. In the fust case, the steps of drying and mixing the dried material in molten bitumen are involved, whereas in continuous operation, the spent material is introduced as slurry to equipment that continuously mixes the bitumen at the same time. Then, the bitumen mixture flows into a suitable storage container and is solidified upon cooling. Neilson and Colombo (1982) have presented the main features of the process for ion-exchange resin wastes. 

Polymer immobilization The polymers used in the immobilization of spent materials can be classified into two main categories thermoplastic and thermosetting polymers. The first type is fed in the form of a solid, and then melts upon heating and combines with the waste. On the other hand, thermosetting polymers are supplied in a liquid form and are then polymerized to a solid form, combining with the waste upon heating or in the presence of catalysts. 

Special reference should be made for the last section of Chapter 3 Particle analysis. Everything in connection with particle properties and basic calculations, irrespective of its specific use, is presented from particle surface area to calculations regarding its terminal velocity and diffusion coefficients. Furthermore, concerning materials used in adsorption, ion exchange, and catalysis, special paragraphs are included in Chapters 4 and 5 as well as the management of spent materials. 

A similar procedure has been used for the regeneration of spent thallium(I) fluoride after fluorination reactions. The spent material can be boiled with ethanol and washed with acetone prior to treatment with hydrofluoric acid. 

Overhead from the chlorinator is scrubbed to remove excess chlorine in two vessels in succession which employ water and 5% caustic solution, respectively. The water from the first scrubber is used in the chlorine solution tower. The caustic is recirculated in order to provide adequate wetting of the packing in the caustic scrubber fresh material is charged in at the same rate as spent material is purged. Following the second scrubber, propylene dichloride is recovered from the gas by chilling it. The spent gas is recycled to the chlorinator in the required amount, and the excess is flared. 

The herbs and spices may be placed in cloth bags and suspended in the wine. After the first extraction, fresh base wine may be added for a second, and even a third extraction. Partial extractions are preferred, as complete extraction may result in the incorporation of undesirable flavors or aromas. This also avoids pressing the spent materials that is associated with the release of objectionable bitter flavors. 

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