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Preparation of alum from scrap aluminium

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Chemistry 244 Experiment 3 - The preparation of alum from scrap aluminium Dian Page 15533670 30 August 2010 Abstract The recovery of aluminium from scrap aluminium through its conversion to potash alum (KAl(SO4)2·12H2O) was investigated. It was found that a final percentage yield of 76% was obtained. In addition a final yield of 9.00g was yielded. Introduction Aluminium, because of its low density, high tensile strength and resistance and resistance to corrosion, is widely used for the manufacture of aeroplanes, automobiles, lawn furniture as well as for aluminium cans. Being a good conductor of electricity, it is used for transmission of electricity. Aluminium is also used for making utensils. The recycling of aluminium cans and other aluminium products is a very positive contribution to saving our natural resources. Most of the recycled aluminium is melted and recast into other aluminium metal products or used in the production of various aluminium compounds, the most common of which are the alums.1 Alum is a salt that is a combination of an alkali metal, such as sodium, and a trivalent metal, such as aluminium.2 & 3 Alums are double sulphates having a general formula (equation 1) more.


Rinse the beaker twice with 5-mL portions of distilled water, pouring each rinse through the filter residue. Buchner filter was used. Dark black residue was left on filter paper, and the clear filtrate was obtained in the flask 7 Transfer clear filtrate to 250 ml beaker + add 10 drops of methyl indicator solution. The solution turned to a yellow colour (before acid is added) 8 Addition of 6 M H2SO4 with constant stirring. On addition of the acid, the solution got hot from a neutralization reaction occurring and a white precipitate of aluminium hydroxide formed. 18 ml of the acid (H2SO4) had to be added and the solution had to be placed on a steam bath so that Al(OH)3 will dissolve. It had a red clear colour. 9 Cool mixture in ice bath White alum crystals formed after a waiting period of 16 min and occasional stirring. 10, 11 and 12 Filter alum crystals Filter was put on longer than usual. (more effective results) White crystals stayed at the top and a pinkish/reddish filtrate was obtained in the flask below. more.


may improve if the reaction could run longer i.e. the flasks placed longer on the steam baths, at warmer temperatures, in the fume hoods and that the filter runs longer so that the product is essentially dry. It is also noted that more H2SO4 had to be added excessively to dissolve Al(OH)3, so maybe in future experiments a super acid could be used for a more effective yield. The reason why this procedure is not used in the industry is because H2 gas burns explosively1 which means it is highly pollutant and on a large scale i.e. a big industry, the pollution will be catastrophic. KOH is also very corrosive so it can attack the machines in the factory, industry, which means it will rust and cost the company a lot of money. Sulfuric acid is also very hazardous. Conclusion The experiment illustrated an interesting example of the reduction of an environmental waste product. In doing so, reducing aluminium to potassium aluminium sulphate dodecahydrate, a final percantage yield of 76% was obtained. It was also found that a theoretical yield of 11.8g should have been yielded if all the procedures were done 100% efficiently, but because this is a practical a final yield of 9.00g was obtained. more.

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