Cable treatment with carboxylic acids

Abstract

Upon reaching the end of their useful life, electrical cables with polyvinyl chloride (PVC) insulation most commonly remain in the ground, or are sent to a landfill, where they accumulate at a rate of about 70,000 tons per year. Therefore, there is an interest in recycling aluminum and copper, which requires various technological cable processing schemes to be developed. Typically, such schemes involve either mechanical stripping, or high-temperature and/or chemical treatment technologies, with the latter utilizing organic solvents (e.g., dichloroethane, acetone, diethyl ether, etc.), capable of dissolving plasticizers contained in the insulation, which leads to an unjustified waste of aluminum and copper. Besides, in combination with newly generated mechanical and flue gas waste, such schemes create an additional serious environmental burden. Therefore, there is an interest in developing an alternative and environmentally friendly cable treatment process by utilizing solutions of weak carboxylic acids (acetic and citric), as well as hot and cold water. It is also important to study the specifics of the process of efficient treatment of protective polyvinyl chloride insulation of cable scrap in weak carboxylic acids, as well as in cold and hot water. The conducted studies involve: treating cable samples in weak carboxylic acids, as well as in cold and hot water; analyzing the kinetics of the sample mass change; and determining mechanical characteristics of PVC insulation. As a result, an increase in strength of the PVC insulation depending on the percentage of swelling was experimentally established. It has been shown that the insulation can be strengthened by about 400–1200%, depending on the type of solution. The kinetics of the PVC insulation swelling was studied for various types of cables. It was shown that their swelling rate constants have fairly close values, which is indicative of a common physicochemical nature of the process of liquid absorption by insulation. A regression-correlation analysis was used to optimize the process parameters of soaking PVC insulation samples in weak carboxylic acid solutions, as well as in hot and cold water. It has been shown that by optimizing the controlled parameters, the level of strengthening of PVC insulation can be increased by 4800–5280%. The corresponding empirical dependences of the PVC insulation strengthening process were obtained in the following form: \(Y=\upalpha _{0}\cdot f\left(x_{1}\right)\cdot f\left(x_{2}\right)\cdot \ldots \cdot f\left(x_{n}\right),\) where the function variables include the percentage of sample swelling; process duration; solution temperature and pH level.