Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Patent
1995-01-13
1997-12-16
Straub, Gary P.
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
75353, 75401, 588209, 588234, 588236, 423 44, 423 88, 423 96, 423107, 4231503, A62D 300, B01D 1100, C01G 900
Patent
active
056987595
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of treating materials comprising or including polyvinylchloride (PVC), chlorinated rubber and other chlorinated polymers.
PVC, especially PVC which is contaminated with other plastics is very difficult to recycle, as on heating, the material decomposes before it melts. It is possible to dissolve PVC in organic solvents, but when other plastics are present these may also dissolve with undesirable effects. With much scrap PVC the only method of disposal is land fill. However, this can be hazardous if the PVC contains toxic metallic fragments, such as copper from PVC covered copper wire. In addition, stabilisers are frequently added to PVC and these may be salts of Sn, Pb, Cd, Zn, Ba, Ca, Cu and Na, some of which form toxic compounds when PVC is heated at elevated temperatures.
As more and more products are recycled, various residues, fluxes and drosses are formed which have no commercial value and have difficult and expensive disposal problems. It is possible to devise chemical ways for treating these materials, but invariably the cost of the reagents and the chemicals makes the processes prohibitively expensive. Furthermore, many of these waste materials have been declared hazardous, and therefore this makes their disposal even more difficult. One example of a substance which is generated and which requires recycling is electric arc furnace dust, which is generated when scrap steel is melted in an electric arc furnace. The dust contains iron oxides and quantities of zinc, lead and cadmium which makes it a toxic material. Known methods of attempting to dispose of the electric arc furnace dust have proved to be unsatisfactory, in that it is very difficult to extract all the zinc, cadmium and lead so that the remaining slags, dust etc are completely safe for disposal. The problem of disposing such materials is likely to get considerably worse in the future when car bodies that have been galvanised are recycled. According to a first aspect of the invention there is provided a method of treating PVC, chlorinated rubbers, or chlorinated polymers comprising the steps of:
combining PVC, chlorinated rubbers or chlorinated polymers at an elevated temperature with an element or compound of an element, the chloride of which element is more stable than an oxide of that element; and
reacting the PVC, chlorinated rubber or chlorinated polymer with an excess of air.
Advantageously, the compound is an oxide.
The PVC, chlorinated rubber or chlorinated polymer will essentially burn in the excess air to generate carbon dioxide and water as well as hydrogen chloride and sometimes a small amount of chlorine. The hydrogen chloride will react with the element or compound of the element to form a chloride.
According to a second aspect of the invention there is provided a method of treating iron contaminated with one or more non-ferrous metals with PVC, chlorinated rubber or a chlorinated polymer, and air or oxygen, wherein the PVC, chlorinated rubber or chlorinated polymer burns the air or oxygen to produce hydrogen chloride, and wherein the non-ferrous metals react with the hydrogen chloride to form volatile chlorides.
The reaction of PVC with air gives off considerable heat and this is more than sufficient to raise the temperature of any component to about 1300.degree. C. The heat may be used to create steam and generate electricity.
Preferably the chloride is condensed. After condensation the chloride may be purified and then electrolysed to form chlorine gas, and metal.
By means of the present invention therefore, not only is a method provided for safely processing PVC, but the method also allows for reclamation of chlorine from waste PVC and the treatment of waste metallic products.
Preferably, the PVC is combined with electric arc furnace dust or some other residue. The dust contains iron oxides and quantities of zinc, lead and cadmium. The fact that the reaction of PVC with air gives off considerable heat ensures that all components in the dust are raised to a temperature of about 1300.degr
REFERENCES:
patent: 4447262 (1984-05-01), Gay et al.
patent: 4800069 (1989-01-01), Fray
patent: 4855081 (1989-08-01), Wallace
patent: 5198018 (1993-03-01), Agarwal
patent: 5541952 (1996-07-01), Gewge et al.
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