NAAIO2 is recovered in the decanted solution
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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![Alumina from bauxite separation stage calculations
A crucial step in the production of aluminum from bauxite ore is the separation of
alumina from the remaining mineral impurities in the ore. In the Bayer process this is
accomplished by treating bauxite with aqueous NaOH to produce NaAIO2 (alumina).
NaOH(aq) + Al(OH)3(s) → NaAIO2(aq) + 2H2O(1)
Since NaAIO2 is water soluble while the residual mineral constituents of bauxite are not,
a separation can be achieved by allowing the minerals to settle out and decanting the
aqueous solution of NAAIO2 and unreacted NaOH. In order to further recover any
NAAIO2 entrained in the settled mineral solids, this "mud" is repeatedly washed with
water and allowed to settle, and the wash water is decanted. The figure below shows
one stage of this washing-settling process.
Wash water
Slurry -
Open to air
Mixer/Wash tank
Setling tank
Decanted solution
System boundary
Washed mud
In this stage, a feed slurry consisting of 10 wt% solids, 11 wt% NaOH, 16 wt% NaAIO2
and the rest water is washed with a wash-water stream containing 2 wt% NaOH to yield
a decanted solids-free solution containing 95 wt% water and a settled mud containing
20 wt% solids. How much NaAlO2 is recovered in the decanted solution if slurry is fed
at the rate of 1000 lb/hr?]](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F63f5865a-7713-44c4-be73-1c5678c4385b%2Fb5e13fac-4b78-4c16-847a-b518d13a95ef%2Fodtnb3_processed.png&w=3840&q=75)
Transcribed Image Text:Alumina from bauxite separation stage calculations
A crucial step in the production of aluminum from bauxite ore is the separation of
alumina from the remaining mineral impurities in the ore. In the Bayer process this is
accomplished by treating bauxite with aqueous NaOH to produce NaAIO2 (alumina).
NaOH(aq) + Al(OH)3(s) → NaAIO2(aq) + 2H2O(1)
Since NaAIO2 is water soluble while the residual mineral constituents of bauxite are not,
a separation can be achieved by allowing the minerals to settle out and decanting the
aqueous solution of NAAIO2 and unreacted NaOH. In order to further recover any
NAAIO2 entrained in the settled mineral solids, this "mud" is repeatedly washed with
water and allowed to settle, and the wash water is decanted. The figure below shows
one stage of this washing-settling process.
Wash water
Slurry -
Open to air
Mixer/Wash tank
Setling tank
Decanted solution
System boundary
Washed mud
In this stage, a feed slurry consisting of 10 wt% solids, 11 wt% NaOH, 16 wt% NaAIO2
and the rest water is washed with a wash-water stream containing 2 wt% NaOH to yield
a decanted solids-free solution containing 95 wt% water and a settled mud containing
20 wt% solids. How much NaAlO2 is recovered in the decanted solution if slurry is fed
at the rate of 1000 lb/hr?]
Expert Solution
Step 1
To separate two different density fluids which are immiscible to each other decantation is only process available. Decantation is also used when liquid needs to be remove from solid. Separating funnel or in large process decant tank is used where the two layers of liquids are settled from which top layer is separated. In case of solids and liquids to separate solids gets settled in bottom from which liquid of top layer is separated.
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