Chemical and Electrochemical Processing of Aluminum Dross Using Molten Salts

Abstract

A novel molten salt process was investigated, where Al, as metal or contained in Al 2 O 3 and AlN, was recovered from Al dross by chemical or direct electrochemical reduction in electrolytic cells. Electrolysis experiments were carried out under argon at temperatures from 1123 to 1243 K. In order to better understand the reduction behavior, the as-received Al dross was simulated using simplified systems, including pure Al 2 O 3 , pure AlN, an Al 2 O 3 /AlN binary mixture, and an Al 2 O 3 /AlN/Al ternary mixture. The reduction of the as-received dross was also studied experimentally. The studies showed that solid Al 2 O 3 was chemically reduced by the Ca in a Ca-saturated Ca-CaCl 2 melt to form Al 2 Ca or electrochemically reduced to Al-rich Al-Ca alloys and that the Al value in the Al 2 O 3 was easily recovered from the Al drosses. It was found experimentally that solid AlN in the drosses could not be calciothermically reduced to any extent, consistent with thermodynamic evaluations. It was also found that the direct electrochemical reduction of the AlN in the drosses was confined to three phase boundaries (3PBs) between the AlN, the electrolyte, and the current collector and could not be enhanced by using the LiCl-containing chloride melt or the chloride-fluoride melts studied. The presence of Al powder in the Al 2 O 3 /AlN mixture facilitated the direct electrochemical reduction of both Al 2 O 3 and AlN. The reduction mechanisms are discussed based upon the present experimental observations. Flow sheets for recovering the metallic Al and the Al in the Al 2 O 3 and AlN from Al dross are finally proposed.

Degeneration of Key Structural Components Resulting in Ageing of Supercapacitors and the Related Chemical Ageing Mechanism

“…The comparison of Al 2p spectra denotes that most of the metal Al on the current collector surface is oxidized into Al 2 O 3 during SCs’ ageing. Besides oxidization, nitridation and carbonization side reactions might also occur in the current collectors that would produce Al 4 C 3 or AlN with poor electrical conductivity. , …”

“…Besides oxidization, nitridation and carbonization side reactions might also occur in the current collectors that would produce Al 4 C 3 or AlN with poor electrical conductivity. 33,34 In addition to electrodes and current collectors, PP separators are definitely not negligible as another key structural component of SCs. The influence of PP separator ageing was also analyzed by XPS and TOF-SIMS tests.…”

Alternative Al production methods

“…Figure 6 shows the E-pN 32 diagram for the Al-N system in a LiCl-KCl eutectic melt at 450uC showing the region where Al solid is stable. Yan (2008) conducted a direct electrochemical reduction of AlN cathode in a CaCl 2 -NaCl melt at 1133 K and observed a pure Al droplet. The yield, however, was low, i.e.…”

Preparation of TiC powders and coatings by electrodeoxidation of solid TiO2in molten salts

“…7,18 Subsequently, the method of direct electrochemical reduction has been successfully applied on a laboratory scale to produce metals and alloys from their oxide precursors, and to recover the aluminium value from aluminium dross. [19][20][21][22][23][24][25][26][27][28][29][30][31][32] In this work, the thermodynamic aspects involved in the process are considered in detail. Experimental results are presented for direct electrosynthesis of TiC powders or coatings from a stoichiometric TiO 2 /graphite powder mixture or TiO 2 coatings on graphite substrates.…”