In order to investigate an alternative process for the production of primary aluminum via a sulfide intermediate, the electrochemical behavior of Al 2 S 3 in molten salt has been studied on a laboratory scale. The effects of electrolyte composition, temperature, and cell design on the cell performance have been investigated. Temperature and cryolite addition have positive effects on the current density. Increasing the anode-to-cathode surface area ͑closer to unity͒ and shortening the interelectrode distance lead to higher current density. It is concluded that the electrolytic process is governed by the ohmic drop, caused mainly by the sulfur bubbles at the anode. © 2007 The Electrochemical Society. ͓DOI: 10.1149/1.2728263͔ All rights reserved.Manuscript submitted October 9, 2006; revised manuscript received February 9, 2007. Available electronically April 23, 2007. In terms of primary energy consumption, the Hall-Héroult process requires about 140 MJ energy to produce 1 kg of aluminum metal, which is about four times the theoretical thermodynamic minimum ͑34 MJ/kg Al͒. Apart from substantial CO 2 and SO 2 emissions from the production of electrical energy as well as the consumption of carbon anodes, the Hall-Héroult process creates greenhouse gas emissions such as CF 4 and C 2 F 6 stemming from the electrolyte that consists mainly of liquid cryolite ͑Na 3 AlF 6 ͒. These and other apparent disadvantages of the Hall-Héroult process have led to numerous research efforts to find an alternative route for primary aluminum production throughout the 20th century.The best investigated alternatives are inert anodes, 1 the use of AlCl 3 as an intermediate step,2 and the carbothermic reduction of alumina.3 Inert anodes would enable a closed cell concept that is more favorable in terms of environment, energy efficiency, and capital cost. The aluminum chloride process comprises the chlorination of Al 2 O 3 to AlCl 3 as an intermediate, and subsequent reduction of AlCl 3 to aluminum in an electrolysis cell. Due to the lower cell voltage required, the carbon anode remains inert and less electrical energy is required compared to an inert electrode process based on the reduction of alumina. Carbothermic reduction would eliminate the electrolysis step altogether, but high temperatures in excess of 2000°C would be required. Despite the substantial amount of capital spent on these and other processes, no proven and economically feasible alternative to the Hall-Héroult process to date exists.Another alternative is to use aluminum sulfide as an intermediate step, named the Compact Aluminum Production Process ͑CAPP™͒. 4,5 In this process, Al 2 S 3 is produced by the reaction of CS 2 and alumina. Subsequently, the aluminum metal can be extracted by electrolysis, producing sulfur gas at the anode, which can be recycled to the production of CS 2 . The simplified reactions ͑as-suming no complex ions͒ of the electrolysis process can be described as follows Due to the lower cell voltage required, the carbon anode remains inert and less el...

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d 25 g of mould powder are cold pressed uniaxially to a cylindrical shape. The pressing force is 20 MPa. The Controlled melting of mould powder on top of the dimensions of the cylinder are 30 mm dia. and approx. meniscus is essential for efficient mould flux 25 mm height. performance. This paper presents two d The cylinder is placed into a furnace at a temperature complementary methods to determine the melting of 1400°C, which is above the melting point of the speed of a mould powder. One method measures mould powder. the displacement of a prepressed cylinder of mould d A rod of alumina (20 mm dia.) is placed on top of the powder at a fixed temperature. This method yields cylinder. As a result of the softening of the mould powder qualitative, but reproducible, results which can be the rod will be displaced. This displacement is registered related to flux composition. In the second method, a as a function of time. sample of mould powder is melted on top of a steelIt should be mentioned that nearly all methods used to bath. The data are interpreted with the help of an obtain the melting speed of mould powders are experimental improved theoretical melting model, resulting in methods based on visual observations. An important advanquantitative values of melting speed and thickness tage of the softening method is that the results obtained of the molten flux layer. The results of both are based on well de ned measured values resulting in methods agree well with measured plant data.reproducible numbers.

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