*7Ae tiÊ&emêmi Aluminum from Clay
First step in the hydrochloric acid process is the roasting of the clay at 700° C. wliich decomposes aluminum silicate, thus permitting the ready solution €ff alumina in hot dilute hydrochloric acid
In the digester shown, the roasted clay is stirred voith dilute hydrochloric acid at 100° C. tchich dissolves the soli&ble material and leaves behind insoluble silica
i£SP
Effects of submarine warfare on bauxite shipments early in the war served to accelerate re— search efforts which resulted in the development of two processes for the recovery of alumina from clay by workers at t h e National Bureau of Standards. Of t h e two, the hydrochloric acid extraction method outlined here has been developed to the pilot-plant stage· The other, an alkaline extraction method using a solution consisting of a mixture of sodium hydroxide and sodium chloride, h a s not progressed beyond laboratory studies· The alumina obtained in the acid extraction method has an average purity of about 99.8%. The only significant impurities are 0.1% chlorine, 0.04% iron oxide, and 0.06% silica. In addition to its use in production of metal the alumina produced by this process is a superior product for polishing metallographic specimens and has also been used with good results in the preparation of enamels for use at high temperatures. The cost of producing aluminum by the hydrochloric acid method i s at present about twice that from imported bauxite. However, studies now in progress may lead to lower costs of production.
Filter press far removal of insoluble-material. The acid filtrate and washings are then evaporated to a smaller volume and transferred to. the precipitator
CHEMICAL
AND
ENGINEERING
NEWS.
Iîecv4 "Panade FLOW HOFFMAN
SHEET
Al203
PROCESS
KAOLIN
I
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FILTER j PRESS SIOt SLUOOE
WASTE H.O
M,0
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WASTE TOWER
Uu
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Γ
STII
Mi
LIOUIO STORAGE
eiccoc* vâLvc ;
«SeCENTRIFUGE
Ml
PRECIPITATOR
GAS LIOUIO SOLIO H4"——ΡΆΙ.Ο. CALCINER
Lender portion of precipitator in which acid filtrate is converted to hydrated aluminum chloride {AlCh'6HA)} by failing against a stream of hydrogen chloride. Aluminum, chloride is separated hy centrifuging
(PROOUCT)
Final step, is the calcination of the hydra~ted ulu,mi*> ~nitm chloride* Here aluminum chloride crystals are fed into the hopper of the Herreshoff furnace
VOLUME
2 5, N O . 2 2
JUNE
2, 1 9 4 7
jtlumina is removed by a vibrating conveyor so ar ranged tiujt the lovcer end of the outlet r is filled %x>ith oxide, thus- preventing the entrance of tsir
1591
