For T a' similar stoichiometric calculation can be made. When S and T 'occur together the amounts of PbO required for each of them are to be summarized. For separating A as far as possible in a quantitative Way from the acid oxides S and T the melt should not contain any appreciable amount of other basic oxides as FeO, CaO, MgO, Na2O, K20 because such oxides, in the presence of A, are able to form aluminates and if S also be present, they are able to form silicatealuminates, which of course implies a decrease of the amount of free A Therefore, if such oxides occur in the raw material to be treated their amount should preferably be decreased before melting with PbO, by some preliminary treatment of the raw material.
Such removal is not necessary however, but is to be preferred as it will result in a higher yield of A An application of industrial importance of this method is the recovery of A from certain raw materials, occurring in nature, for the production of Al. Other ranges of application also occur, as will be mentioned in the following. Raw materials occurring in nature containing Al, which are suitable for treatment by this method are primarily bauxites, clays and latherites.
Fe can be removed almost completely by means of several known processes amongst which may be mentioned reduction to FeO, followed by leaching with acid, reduction to E and magnetical separation, or removal in chlorine gas. The hydrate water can be removed as vapour by heating to at least C. It may be mentioned that T can be removed by some similar preliminary treatment as for instance in a stream of chlorine gas, according to what is already known. Si02 and Pb0.
Ti02, or, better, so that 2Pb0. Si02 and 2Pb0. T are formed. After melting together at a temperature of C. For facilitating the enrichment of the lighter A towards the top of the melt, a slow cooling by which A falls out of solution can be followed by a rapid heating when A rises in the liquid mass. This cooling and heating can be made in the moulds or even in the melting furnace.
Sodium metal is not easy to obtain either. As a result some of the earliest aluminum metal was made into jewelry. The purified aluminum oxide is mixed with cryolite, a mixture of sodium fluoride and aluminum fluoride, and heated to about degrees Celsius to melt the solids.
The mixture melts at a much lower temperature than aluminum oxide would by itself. The hot molten mixture is electrolyzed at a low voltage of volts, but a high current of 50,, amps.
Aluminum ions are reduced to aluminum metal at the cathode the sides and bottom of the electrolysis cell.
At the anode, oxygen is produced from the oxide ions. Both the negative electrode cathode and positive electrode anode are made of graphite, which is a form of carbon.
Aluminium ions receive electrons at the negative electrode and are reduced to aluminium atoms :. The molten aluminium sinks to the bottom of the cell, where it is tapped off. Oxide ions lose electrons at the positive electrodes and are oxidised to oxygen gas:. This oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide, so they gradually burn away. During electrolysis:. The oxygen reacts with the carbon in the electrodes, forming carbon dioxide which bubbles off.
Carbon is therefore lost from the positive electrodes, so they must be replaced frequently. This adds to the cost of the process.
Extracting metals using electrolysis Metals are found in ores combined with other elements.
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