Monthly alumina output in China rose significantly in March, revealed first-hand production data of the Chinese alumina refines factory as surveyed by the Shanghai Metals Market. Alumina production volume last month totalled 5,831,000 tonnes, up 27 per cent from March 2016 and +12.45 per cent from February this year. February’s total alumina output was estimated at 5,185,000 tonnes.
During the initial three months of 2017, that is, from January-February China produced 16,600,000 tonnes of alumina. The volume is 24 per cent higher than alumina produced in the corresponding period previous year.
According to SMM estimate, April alumina output in China domestic market will decline by 2.48 per cent month-on-month to stand at 5,686,000 tonnes.
China’s primary aluminium output in March rose 23 per cent from the previous year to total at 3,112,000 tonnes. The cumulative production for the first three months of 2017 was estimated at 8,988,000 tonnes, up 22.1 per cent from the same period previous year. In April, China is estimated to produce 3,041,000 tonnes of aluminium, down 2.28 per cent MoM.
The electrolytic purification is carried out preferably in the form of the well known three-layer electrolyte process which has been employed by the aluminum industry for a very long time, or by means of the bipolar electrolyte cell described in the U.S. patent application Ser. No. 630,289. A bipolar cell is employed in particular if the scrap aluminum has a high concentration of silicon and/or iron, as the large losses in copper occurring in the three-layer process can be avoided.
The amount of salt required for carrying out the process according to the invention is calculated such that it is preferably 1.2-2 times, in particular 1.5 times, as large as the weight of scrap to be purified. The charges of salts employed comprise, usefully, of 30-50 wt % NaCl, 30-50 wt % KCl and 15-25 wt % cryolite. A melt that has proved particularly advantageous contains about 40 wt % NaCl, 40 wt % KCl and 20 wt % cryolite, said melt being held at a temperature of about 750° C. before the pre-heated scrap aluminum is added to it. Especially when the scrap is in small pieces it can be advantageous, before holding, to stir the molten mixture of salts and scrap aluminum. The main effect of this is to lower the concentration of magnesium in the aluminum scrap. The stirring is achieved by known mechanical means, for example using a magnetic stirrer or by injection of inert gases.
The purifying action of the salt melt can be increased by employing a conventional scrubbing gas such as chlorine before holding.
During holding, which lasts preferably 1-2 hours, droplets of aluminum sediment to the bottom of the holding vessel, for which the melting furnace also usefully serves.