Crushed waste forms

The PCT was conducted on crushed waste form samples from supernatant and sludge. The fineness of the particles, compared with what is prescribed in the test procedure (see Section 17.4.1), was recognized from the beginning, and hence the actual measured... 

The samples were stored for 3 weeks for curing. Each sample was then crushed and was subjected to the TCLP test. The TCLP test results on both the waste stream and the treated CBPC waste form are given in Table 16.6. The results on the untreated waste streams show that the leaching levels far exceed the regulatory limits. The results for the waste forms, on the other hand, are an order of magnitude below the EPA limit. These results indicate superior stabilization of Hg in the phosphate ceramic waste forms coupled with sulfide immobilization. 

High-permeability passive perimeter gas control systems entail the installation of highly permeable (relative to the surrounding soil) trenches or wells between the hazardous waste site and the area to be protected (Figure 16.6). The permeable material offers conditions more conductive to gas flow than the surrounding soil, and provides paths of flow to the points of release. High-permeability systems usually take the form of trenches or wells excavated outside the site, then backfilled with a highly permeable medium such as coarse crushed stone. 

Many cements used today are composites of Portland cement and industrial waste materials that can enter into the hydration reactions and contribute to the strength of the hardened product. These substances include pulverized fuel ash (PFA) from burning of pulverized coal in thermal power stations, crushed blast-furnace slag (Section 17.7), and natural or artificial pozzolanas—that is, volcanic ash and similar finely particulate siliceous or aluminosilicate materials that can react with the Ca(OH)2 in Portland cement to form hydrated calcium silicates and aluminates. As noted earlier, the solubility of Ca(OH)2 is such that the pH of pore water in Portland cements will be about 12.7, at which the Si-O-Si or Si-O-Al links in the solid pozzolanas will be attacked slowly by OH- to form discrete silicate and aluminate ions and thence hydrated calcium silicate or aluminate gels. 

On the basis of experiments carried out using a laboratory size fluid bed combustor it has been demonstrated that, provided certain precautions are taken, crushed slag and other wastes from conventional coal-burning furnaces can, in the mrgority of cases, be burnt with the recovery of worthwhile amounts of energy and with less environmental pollution from SO2 and NO emissions than could result from the combustion of an equivalent amount of coal. The ash produced has a very low carbon content and is granular in form. 

The most economical pressure agglomeration method, which is also applicable for a wide range of capacities, uses roller presses (see Section 4.2.2.4). Depending on the surface configuration of the rollers, either compacted sheets are produced which are subsequently crushed and screened into a granular product or, if the rollers are pocketed, briquettes are formed. For waste treatment and the production of secondary raw materials (recirculation of valuable components) the latter is often preferred. Briquettes are usually pillow shaped and almost monosized, featuring a volume that may typically range between 20 and 100 cm3. 

For brittle materials, shear force is restricted to hammer mills, acting along with impact and attrition, as well as to toothed crushing rolls. The prerequisite for successful size reduction of particles is the existence of macro- or microstructure weaknesses (e.g., layered structure, schistosity) or differences in the characteristics of adjacent minerals (e.g., hardness, friability). Contrary to rocks and minerals, shear force is widely applied in soUd waste size reduction, as most of its constituents are soft, nonbrittle, plastic, and ductile, and, consequently, shear forces are effective. The various forms of shredders use shear force to reduce the size of solid waste constituents. 

Mechanical stability. When a block of solidified waste is crushed by mechanical impact, fragments of various size will be formed. Two consequences are to be considered (1) The fraction of radioactivity leached in a certain period of time will be increased in proportion to the increase in surface area (2) the formation of very small particles in the order of 100 jum and less may enable radioactive material to be spread by air. Even larger particles may be carried by water. 

Natural convectional dryer has been used in Philippines to produce dried sweet potato. These dryers utilize heat from burning the wastes. About 50 kg of sweet potato chips of high quality are dried for 7-8 h. Another form in which sweet potato is dried and eaten as a dessert or snack is as an edible leather also known as fruit roll or crush. In this preparation, the flesh of sweet potato is cooked, mashed, and sieved, mixed with 0.5% (w/w) carboxymethyl cellulose (a binder), 200 ppm sodium bisulfite, and 7% (w/w) sugar and formed into a sheet 1-mm thick, which is oven-dried at 55°C-75°C and I0%-17% moisture level. Samples dried at 75°C were chewier than those dried at lower temperatures. Samples were crisper and crunchier when dried at 55°C or 65°C. A laboratory-scale high-temperature short-time (HTST)... 

The yield of retained fraction in the case of irregularly shaped particles was found to be 1.3-1.5 times that for particles with a rounded shape. In crushing operations, for example, particles of barite, quartz, feldspar, and magnetite form rounded particles, decreasing their adhesion. The wastes from low grades of asbestos contain irregularly shaped mineral dust particles, which adhere to the drum surface and are separated as the retained fraction [137]. 

The ore is initially crushed from rock matrix to mineral grain size or smaller. Often this rock powder is mixed with water and/or chemical reagents to form slurry. This mixture is injected with air and agitated by stirring. The mineral particles then attach themselves to air bubbles and float off as a concentrate, while the wet grains of rock (waste) sink to the bottom. 

Tailings and slimes dams represent the waste product after crushing, grinding and processing of the ore. Deposition can be in a dry form or hydraulically emplaced in the impoundment. Traditionally these dams are a major source of potential problems from escape of contaminants into the environment. For example a polymetallic sulphide ore can generate elevated anions, cations and metals together with chemical reagents from the process. 

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