RESUMO
The objectives of this work were to develop polyacrylonitrile nanofibres modified with the commercial Cyanex 272 extractor and apply them for the recovery of gallium present in aqueous solution. The nanofibres were produced using the centrifugation technique, employing Forcespinning® equipment. The average nanofibre diameter ranged from 530 to 840â nm. The highest adsorption of gallium was achieved at pH 2.5, with a pseudo-second order kinetic model and the Freundlich equilibrium isotherm model providing the best fits of the experimental data. The thermodynamic parameters showed that the adsorption was spontaneous, favourable, and endothermic. The maximum capacity of the PAN/Cyanex 272 nanofibres for the recovery of gallium was 38.93â mg g-1. In successive reuse cycles, the nanofibres showed a small decrease of the adsorption capacity for the metal after the first cycle, while the efficiency remained constant in the subsequent cycles. The desorption efficiency remained constant throughout the cycles, with values in the range 80%-90%. The findings demonstrated that PAN/Cyanex 272 nanofibres have excellent potential for use as adsorbents, providing good capacity for the recovery of gallium and satisfactory stability during reuse in several cycles.
Assuntos
Gálio , Nanofibras , Poluentes Químicos da Água , Resinas Acrílicas , Adsorção , Cinética , Ácidos Fosfínicos , Termodinâmica , Poluentes Químicos da Água/análiseRESUMO
This work aims to perform a comparative study of two mechanical processes for the recycling of metals from coaxial cables (aluminium and copper-clad steel): Process I - comminution, sieving and electrostatic separation; and Process II - comminution, magnetic separation and electrostatic separation. Characterization techniques were performed on the cables to discover their composition. The parameters evaluated of electrostatic separation were: roll speed (n), electrostatic electrode distance (D2), voltage applied to the electrodes (U) and splitter angle (γ). The best conditions for electrostatic separation were: Process I - n = 30â rpm, D2 = 8â cm, U = 30â kV and γ = 0°; Process II - n = 10â rpm, D2 = 10â cm, U = 25â kV and γ = 2.5°. Process I presented aluminium with purity of 99.51% and recovery efficiency of 94.53%, as well as copper-clad steel with purity of 96.79% and recovery efficiency of 99.68%. Process II presented aluminium with purity of 96.51% and recovery of 70.12%, as well as copper-clad steel with purity of 99.53% and recovery of 99.46%. A simplified economic assessment was performed on both process, and Process I has demonstrated to be the most profitable for coaxial cable recycling. The results showed that Process I is promising for the recovery of metals from cables due to its simplicity and lower cost, being capable of wide application to other processes that contain a mixture of conductive and non-conductive particles.
Assuntos
Alumínio , Cobre , Fenômenos Mecânicos , Metais , ReciclagemRESUMO
In this work, chitin (CTN), chitosan (CTS) and activated carbon (AC) were used as adsorbents to recover valuable metals from leachates of mobile phone wastes. The mobile phone wastes (contactors) were collected and characterized. The valuable metals were extracted by thiourea leaching. The adsorption of valuable metals from leachates was studied according to the kinetic and equilibrium viewpoints. It was found that the contactors were composed by Au, Ni, Cu and Sn. The thiourea leaching provided extraction percentages of 68.6% for Au, 22.1% for Ni and 2.8% for Cu. Sn was not extracted. The leachate presented 17.5 mg L-1 of Au, 324.9 mg L-1 of Ni and 573.1 mg L-1 of Cu. The adsorption was fast, being the equilibrium attained within 120 min. The adsorption of Au, Ni and Cu onto CTN and AC followed the Langmuir model, while, the adsorption of these metals onto CTS, followed the Freundlich model. Removal percentages higher than 95% were obtained for all metals, depending of the type and amount of adsorbent. It was demonstrated that the adsorption onto chitin, chitosan and activated carbon can be an alternative to recover valuable metals from leachates of mobile phone wastes.