chemistry and the environment
Recycling of Sodium Waste Bettina Hiibler-Blank, Michael Witt, and Herbert W. F40esky1 institut fur Anorganische Chemie der Universitat, Tammannstrasse 4, D-3400 Gottingen Dry solvents are oRen essential in chemistry for analytical as well as synthetic purposes. The drying process for many solvents (e.g., ethers, hydrocarbons, tertiary amines) requires metallic sodium, as wire or in compact lumps ( I ) . Large amounts of unreacted sodium remain after these operations. These residues are normally destroyed by alcoholysis and therefore must be stored in a deposit for hazardous waste, at considerable expense. Sodium can be recovered up to 90% using the procedure described below. In addition to a remarkable decrease in cost, this recycling process makes a substantial contribution in diminishing or avoiding waste. The Procedure Gathering Sodium Wastes The handling of sodium requires special care. Safetyinstructions are descrihed inHazards in the Chemical Laboratory (2). Caution: The gathering and recovery of sodium must he done in a separate fume hwd to avoid dangerous reactions with other chemicals.
Sodium Woste B Mineral O i l
1 -
O i l Bath
Figure 2. Melting process
.Caution:
Author to whom correspondence should be addressed.
After removal of residual solvents the remaining impure sodium is transferred into the melting apparatus (Fig. 1) and covered with mineral oil. Experimental Instruction 'Caution: The sodium-containingwaste must always be covered with mineral oil. For recovery of sodium in a vessel (diameter: 10 cm; length: 20 cm; wall strength: 2 mm) about 500 g of waste are added to 10&150 mL of mineral oil. The vessel (Fig. 2) is heated in a n oil bath to just over 100 T. Melting During the melting pmcedure the sodium waste is compressed several times using a thick, flattened glass rod. After eomplete melting, the sodium forms a single layer below the mineral oil. The nonreusable residues, that is, the impurities of higher density, settle down a t the bottom of the vessel. Separation and Removal A stainless steel cylinder (diameter: 9 em; length: 15 cm) with a removable handle is dipped slowly into the melt (Fig. 3). The molten sodium and the mineral oil enter through a 2-mm hole in the bottom (Fig. 4). The metal ves-
Figure 1. Melting apparatus.
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Figure 3. Steel cylinder,
Steel Cylinder
Sodium
Waste
Figure 5. Discharge of sodium block.
Figure 4. Resolidification of sodium. sel is carefully dipped into the melt (but not too deeply) so that no sodium flows over the edge. Afterwards the pot is fixed, and the system is cooled to ambient temperature. Then the mineral oil is decanted. (It can be reused.) The steel cylinder with the resolidified sodium is removed from the reaction vessel. After removing the handle, a sturdy wire (diameter: 1.5 mm) is inserted through the hole in the bottom, and the sodium is removed from the cylinder (Fig. 5). Recovery of Sodium from Waste The sodium blockis stored in a vessel that contains high boiling petroleum. The sodium can now be used again for drying. The unrecovered sodium and the hydroxide waste are treated with ethanol and then with water. The sodium hydroxide solutions are collected and stored in a deposit for hazardous waste.
Calculation of Expenses We have successfully recycled the sodium used by a 30-member research team and the students working in an advanced synthetic inorganic class (held twice a year for six weeks with about 30 students).The recycling procedure has decreased the amount of sodium purchased for drying by 7540%. Furthermore, the alcohol consumption is drastically decreased. Normally 10 L of alcohol are needed to treat 500 g of sodium waste. With this procedure, only about 100 mL of alcohol are needed for the waste that contains the unrecovered sodium. In addition to saving the cost of the sodium and alcohol, the expenses for the deposit of waste are reduced considerably by minimizing the amount of waste. Also, the environment is protected.
Literature Cited 1. Fieser, L. Exppnme"t3 in o r p i e chomistv, 3rd ed.; D. C. Heath: Msssaehusetts, 1956. 2. Bmtheriek. L. Xolordr in the Chemlml Loborofory, 3rd ed.: The Chemical Soeiehi: London,1981.
Volume 70 Number 5 May 1993
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