Nourreddine Menad

Combustion of plastics contained in electric and electronic scrap

Abstract Plastic materials have been associated with electric and electronic applications since the early days of the electrical industry. Plastics can amount up to 30% of the scrap mass. Generally, they contains flame retardants such as halogenated compounds which can lead to the formation of different toxic products. Recycling, incineration and landfilling are the current methods used to treat these plastics. They also can be used as combustibles in some metallurgical processes. However, during their combustion, halogenated flame retardants can produce dibenzop-dioxins and dibenzo-furans.

Cathode ray tube recycling

Lead and polybrominated flame retardants are the two hazardous materials that can be found in electronic appliances. Particularly, cathode ray tubes (CRT) contain leaded glasses. In a computer monitor, over 98% of the lead is in the CRT. This material is generally not accepted for reuse as a component; only those from televisions can be reused. However, this currently represents only a very small market. Envirocycle (a US company) has developed a process to recycle all glasses contained in CRTs; this process includes cleaning and sorting glass. The product obtained is used for the manufacture of new CRT glass. Some industries have used pulverized glass from CRTs in smelting processes as slagging material instead of sand or slag. In this paper, some environmental issues related to the recycling of computers and television sets, and CRTs from computers are presented and discussed. Different processes used to recycle CRTs are described along with an economic analysis.

Study of the presence of fluorine in the recycled fractions during carbothermal treatment of EAF dust.

Carbothermal treatment tests of electric arc furnace dusts (EAFD) using the Waelz kiln process were carried out in pilot-scale for the production of zinc oxide. The association of halides in the EAFD, and the recycled products, such as zinc oxide fumes and high-grade iron contents fractions were examined by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM) analysis. XRD reveals the presence of chlorine and fluorine in the dusts in the form of KCl, NaCl and CaF2. An ultra-pure fraction of zinc was obtained after the Double Leaching Waelz Oxide (DLWO) process was performed on the zinc oxide fumes. The halide contents were reduced to approximately 100 ppm Cl and 700 ppm F. The rest of these elements are in the form of CaF2. About 65% F is volatilised as lead and zinc fluorides, 15% is expected in the magnetic fractions and 20% in non-magnetic fractions as CaF2 and MnF2, respectively.

Thermodynamic evaluations on the formation of dioxins and furans in combustion gas

Abstract The formation of toxic PCDD/Fs are discussed thermodynamically for COHCl quaternary combustion gas to elucidate the effects of temperature and gas composition. In most cases, these toxic gases are formed at a temperature below 400°C, representing the isomers of furans and tetra dioxin (4CDD) in similar amounts, but those of other dioxin isomers are much lower.The amounts of PCDD/Fs species formed depend greatly on the gas composition, but are always associated with the formation of chlorobenzenes. When the system contains excess oxygen such as O/C > 1, PCDD/Fs decrease sharply.Hydrogen and water vapor are quite effective in decomposing dioxins and furans to form benzene and hydrocarbons. The derived amounts of PCDD/Fs are much higher than those observed in practice because of kinetic reasons. Taking account of kinetic factors, reasonable amounts of these toxic gases are derived.Especially, the reaction of carbon deposition has always been neglected in thermodynamic calculation of PCDD/Fs because of kinetic reason, but both of solid carbon and PCDD/Fs must be coexisting in small amounts.

Polyvinyl chloride used as a chlorinating and a reducing agent

Abstract Polyvinyl chloride (PVC) or vinyl is a recyclable material. It can be used as a chlorinating and a reducing agent. Two tests of chlorination and reduction of two different samples of jarosite and hematite were realized using PVC, results are presented in this paper. The chlorination test shows that the HCl gas produced from PVC and heated at ≈250°C can be used as a chlorine source to recover as chlorinated compounds the valuable metals such as Zn, Pb contained in jarosite. The XRD reveals the presence of lead and zinc chlorides in the condensates obtained. The second test of reduction was conducted using a mixture of PVC and hematite treated in a nitrogen atmosphere between 200 and 1000°C. The results show that at low temperature, PVC produces HCl and with kinetic consideration, no reactions can be observed with hematite. However, at high temperature, the weight of the hematite sample decreases by ≈15%, due to the reduction of hematite to iron metal.

Kinetics of chlorination and carbochlorination of lead sulfate

The kinetics of chlorination and carbochlorination of PbSO4 with Cl2 + N2 and Cl2 + CO + N2 gas mixtures has been studied using thermogravimetric measurements in the range 700–900°C. The chlorination reaction rate of PbSO4 with Cl2 + N2 increases with rise in the chlorine content in the gas mixture. The reaction order is about 0.66 with respect to chlorine. The chlorination rate of PbSO4 is controlled by a chemical reaction mechanism with an apparent activation energy of about 174 kJ/mol. In the same temperature range, the apparent activation energy of the carbochlorination of lead sulfate by Cl2 + CO + N2 gas mixture is about 114 kJ/mol. The reaction order is about 0.72 with respect to Cl2 + CO. The maximum reaction rate is obtained by using a carbochlorinating gas mixture having a Cl2(Cl2 + CO) ratio equal to about 0.6.

Thermal treatments of industrial wastes in controlled atmospheres for the elimination of As, Hg, Cd, Se and the concentration of Pb, Cu and Zn

Thermal treatments of five different types of non-ferrous metallurgical wastes, under a controlled atmosphere, were carried out at temperatures lower than 800°C for the separation of their toxic compounds and the concentration of valuable metals in the treatments residues. The best results were obtained by the treatments in air or hydrogen, or both successively. Simple treatments, using air or hydrogen, of three samples allowed the elimination of more than 95% of their toxic elements and almost doubled their valuable metals concentration. For the rest of the samples, a combined treatment was necessary for their efficient decontamination. In this case, the valuable metals content in the treatments residue was increased to a reasonable value. Most of the solids issuing from these treatments can be recycled in current non-ferrous metallurgical processes.