United States Patent [19]
Reynolds et ale
[11]
[45]
4,159,310
Jun. 26, 1979
[54]. PROCESS FOR RECOVERING ALUMINUM
AND OTHER METAL VALVES FROM FLY
ASH
[75] Inventors: James E. Reynolds, Golden; Alan R.
Williams, Denver, both of Colo.
[73] Assignee: Public Service Company of New
Mexico, Albuquerque, N. Mex.
[21] AppI. No.: 873,400
[22] Filed: Jan. 30, 1978
[51] Int. C1.2 COIG 23/02; COIF 7/56;
COlG 49/10; COlB 33/08
[52] U.S. C1 423178;'423179;
423/76; 423/135; 423/136;423/149; 423/343;
423/155; 423/166; 423/481
[58] Field of Search 423176, 135, 136, 149,
423/343, 77, 78, 79; 75/112
16 Claims, 11 Drawing Figures
Primary Examiner-Herbert T. Carter
Attorney, Agent, or Firm-Sheridan, Ross, Fields &
McIntosh
A process for recovering aluminum from fly ash containing
iron, silicon and titanium which comprises: (a)
chlorinating the fly ash in an oxidizing atmosphere to
selectively chlorinate and vaporize iron chloride from
the remaining chlorides, (b) chlorinating the residue
from step (a) in a reducing atmosphere of carbon monoxide,
in the presence of added silicon chloride to suppress
the chlorination of silicon, and vaporizing the
chlorides of aluminum, silicon, titanium, and the residual
iron, (c) separating and recovering the vaporized
chlorides by selective condensation, and treating the
residue of step (b) with sulfuric acid to convert calcium
chloride to gypsum, and to regenerate a chloridizing
and binder solution for pelletizing fly ash feed.
Muggleton et at 423/136
Nowak et aI 75/29
Nowak et aI 423/136
ABSTRACT
8/1932
4/1966
9/1969
1,875,105
3,244,509
3,466,169
[57]
References Cited
U.S. PATENT DOCUMENTS
7/1915 Kugelgen et aI 423/136
9/1926 Dearborn 423/136
11/1926 Dearborn 423/136
7/1932 Staib 423/136
1,147,832
1,600,216
1,605,098
1,866,731
[56]
BOIl.ERS MAGNETITE
. RECYCl.E
PELLETiZI NG
__SOl.UITiON
u.s. Patent Jun. 26, 1979 Sheet 1 of 8 4,159,310
MAGNETITE
FIG I
BOILERS
+ • FLY ASH DRY STORAGE (OPTIONAL) ~ MAGNETIC
HOPPER .. HOPPER SEPARATION
• AIR--. I-+ATMOS.
PE LLETI ZING
PELLET PELLET PILE
FUEL--.
DRYING ~---, STORAGE
J
t }-"--I I
OXIDATIVE I--------~-.J r-- REDUCTIVE
CHLORINATION CHLORINATION
(BATCH) (BATCH) ..
eyE L--_ 12 J I 1 H2SO4
1 1i
J
I
CONDENSER I RESIDUE
220°C ) CO2 GENERATOR I LEACH
I I L_--, 1_--/~__---l
H2°1 • I I 1
FeCI3
PREHEAT
WET L1QUID/ SOLID
PRODUCT
COMBUSTION SO~~ SEPARATION
CHAMBER DISPOSAL
FutLAtR STEAM~
CON DENSER CONDENSER
MULTIPLE
EFFECT
-20°C ~ 90°C EVAPORATOR
SiCI4 IREC'tCLE ~f~,'~ TiCI4, CO~C02
FRACTiONAL PRESSURE C12-
DISTILLATION
FeCI3 Df STILLATION MAKE UP
TiCI4 250°C
r-utfLiID
STE+AM
TO SCALE RECYCLE
I SiCI4
SiC'4 SiCI4 AICI 3 ~TO PELLETIZING
STORAGE ~UID STORAGE SALE SOLUTION
TO SALE I L.- __ , L ______.____
u.s. Patent Jun. 26, 1979 Sheet 2 of 8 4,159,310
IOOr------------------.
90
Cl 80
UJ
!::! 70
!;(
..J 60
~
~ 50
UJ
~ 40
..J
UJ 30
lL o'*' 20
10
o
500!=--~'!::-=----=:±-=---~~'--~~--=":=-'",."
FIG 2
o 70r--------::::::::::::='\O
UJ
!:::! 60
:'"5"" 50
~
Iz- 40
UJ
:E 30
UJ
..J
UJ 20
lL
o 10
~
AI
o Si
0~--d.---~2~:......-~30
el2 STOICH 10METRY
FIG 3
u.s. Patent Jun. 26, 1979 Sheet 3 of 8 4,159,310
40L.---I----L-..I--'--_L.---L_....L.-_..L---I._...l
o 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
CHLORINE ADDITION
(FACTOR TIMES THAT REQUIRED FOR A1203)
90
..... Fe
0 80
UJ
N
::J • 750·C
~ / 0
...J ..... AI
0>
70
~z
UJ
::E
UJ
...J
UJ
I.L. 60
0 /
~
Si
FIG 4
u.s. Patent Jun. 26, 1979 Sheet 4 of 8 4,159,310
40 0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0
CHLORINE ADDITION
(FACTOR TIMES THAT REQUIRED FOR A1203)
FIG 5
u.s. Patent Jun. 26, 1979 Sheet 5 of 8 4,159,310
100
90
80
70
z
0
I- 60 «
N
::J
I«- 50
...J
0
>40
~
0
30
20
10
G,
0
700
100
90
G ----0Si
800 900 1000 \lao
CHLORINATION TEMP. °c
FIG 6
o
UJ
~Z
CE
9:x: u
Iz
UJ
:2
~
UJ
~30
Si, 950 AND 10500 C
10
o0~--~l===-:!5:--<l-Cr---"7!:10:-----0:1~5-----::-'20
VOL.% SiCI4 IN REACTION GAS
FIG 7
u.s. Patent Jun. 26, 1979 Sheet 6 of 8 4,159,310
1001,...------------------.
Si,no
SiC I...
Si UNDER 3-7
VOL % SiCI4
80
Ol--__~-_o-..."._I_-_o____:...J--_o____,..J
700 1100
20
90
10
ow
70
!;(
z
a: 60
9
::I: o
I- 50
zw
~ 40
-w'
#.30
FIG 8
u.s. Patent Jun. 26, 1979 Sheet 7 of 8 4,159,310
90
10
20
100 ....-----r---,r---r---,--.,----,---.,----,--.----,--,-----,
Fe(2)@--_-- ~I)
0Fe(3)
80
o~
70
...J
!< 60 ...J o>
I- 50
z
1IJ
~ 40 lJJ
...J
1IJ *30
..--0 _____ Si (I)
OSi(2) -----
Si(3)~
OLO---iIL-..J2L-..J3-..J4--!:5---!:6--::!:7-~S-~9-~-7;~12
C'2 STorCHIOMETRY (FOR AI)
FIG 9
u.s. Patent Jun. 26, 1979 Sheet 8 of 8 4,159,310
-.-----./-
//
./
/
I
/
. / /
/ I .
/.
O~_I-----JL..------.A..,--..I..:----=,"=:----=l:---:::f-=---=-=-~
o 10
a
~80
..J
!(( 60
...J o>
z40
oa:
~ 20
o L.-.:..-..;L.----l_--'--...,......L---:L::--::I-:---==--;;!-::-__=_'.
o 10 20, 30 40
% ALUMINA
60 .------r---....---r----,----r----r--.--..-----,
FIG II
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
2
Improvements are forming the feed material into
carbonfree briquettes, and introducing silicon chloride
into the reductive chlorination step to further suppress
the chlorination of silicon.
The invention will now be described with reference
to the accompanying drawings and examples.
Referring to FIG. 1, the fly ash accompanying the
combustion products ofthe boilers heated by burning of
pulverized coal is collected in a fly ash hopper. The
particular fly ash used in the examples set forth below
was recovered from power plants using San Juan coal
from the Four Comers area of the United States. Of
course, the metal value content of the fly ash will vary
depending upon the area in which the coal was mined.
4,159,310
1
PROCESS FOR RECOVERING ALUMINUM AND
OTHER METAL VALUES FROM FLY ASH
BACKGROUND OF THE INVENTION 5
Large quantities of fly ash carried by the combustion BRIEF DESCRIPTION OF THE DRAWINGS
products of power plants burning pulverized coal exist FIG. 1 is flow sheet of the complete process of the
throughout the country and more is being created by invention.
operation of these plants. This accumulation creates a FIG. 2 is a graph based on test results of oxidationdisposal
problem and representS a waste ofmetal values, 10 chlorination of fly ash in which iron recovery is plotted
particularly aluminum, as a typical fly ash contains up against temperature.
to fourteen percent aluminum by weight. Lesser FIG. 3 is a graph based on results of oxidationchloriamounts
of iron, titranium and other useful metals are nation offly ash at 800' C. in which Fe, AI and Si recovpresent
in fly ash. ery is plotted against chlorine stoichiometry.
No satisfactory process exists for economically re- 15 FIG. 4 is a graph based on test results of fly ash in
covering aluminum from fly ash having the required which metal recovery is plotted against chlorine
purity for commercial" sale because of the difficulty of amounts at ~emperatur~ of 750' ?:-850' C. ~~owing
separating it from other metals present in the fly ash, perce!1ts ,?f Iron, ~umm~ an~ silicon ,:"olatihzed as
particularly, iron. Separation through the chlorination chlond~ m reductiv~ chlonnatlon for vanous ~ounts
route to recover aluminum as aluminum chloride looks 20 ofchlonne added usmg samples of fly ash which had
attractive, however, the process must produce an alumi- first been ~ubjected t? oxidative chlorination.
num chloride of substantial purity. For example, purity ~G. 5 IS a ~aph like t~at of FIG. 2 based on results
requirements for aluminum chloride feed material to an obtained ~t 950 C.-1050 C.
Alcoa-type aluminum cell limit the Ft:203 content ofthe . FIG. 6 !S a .gra~h based on test results of CO reducfeed
to 0.03 percent. Furthermore, in the chlorination 25 tive chlonnation, m.the absence. of ~arbon, ~rf~rm~d
hl . . f d tal h on samples first subjected to OXidative chlonnatlon m
process, the c onnatlon 0 unwante me s, suc as hi h t I tiliza·t' fAl ... F d S'
ili· be d . h . w c percen vo a Ion 0 ,remammg e an I
s con, must suppresse to restnct t e consumption . I tt d . t t tur th hl' t' hi
f hl · h' h bee hib' IS poe agams empera e, e c onne s OIC ome-
~ c onne;?t erwlse, t e process omes pro 1- try for aluminum being within the ranges disclosed in
tlvely expensIVe.. . . 30 the specification.
A further problem mvolved m reco,:"e~g the me~ FIG. 7 is a graph based on results similar to those on
value~ from fly ash. through t~e chlonnation rout~, IS which FIG. 8 below is based in which percent ofAI and
the d~~~l of alkali and .alkalme earth metal chlondes Si chlorinated is plotted against volume percent of
remammg.m the. fI~al re~ld~e.. .. . added SiC4.
Acco~dingly, It IS a pnnclpal 01;'Ject of t~ mventlon 35 FIG. 8 is a graph based on results of CO reductive
to p~ovlde .a meth?d for recovenng alummum of s~b- chlorination in the absence of carbon and in the presstantl~~
y m,gh punty. ~rom ~y ash and '?ther matenals ence of SiC4 in which percent element chlorinated is
con~g Iron an~ sihca Wl~h !he al~um.. plotted against temperature and showing the suppres-
It IS another obJ~ct of this ~ve~tlon t~ 'prOVide a sion of silica chlorination at a volume percent of SiC4
method .for supp~essmg the c~onnatlon ~f silicon when 40 under 3-7, the chlorine stoichiometry being similar to
recoverl.?g ~um1nUm"as alummum chlonde from fly ash that of FIG. 6. The graph illustrates the pronounced
by c~onnatlon.. .,. . reduction in silica reactivity with chlorine. At all tem-
It IS a further o~Ject of this m,:"ention to l?roVlde a peratures tested from 750' C.-1050' C. silica was commethod
for. the dlsp?~ ~f alkali and ~kalme e~h pletely suppressed by injecting as little as 3.5 volume
metal chlonde~ re~ammg m the fmal reSidue r~sultmg 45 percent of silicon tetrachloride.
from the chlonnatlon of fly ash to recover alummum as FIG. 9 is a graph of results from reductive chlorinaaluminum
chloride. tion in which percent element volatilized is plotted
SUMMARY OF THE INVENTION against chl?rine stiochiometry for al~um.
FIG. 10 IS a graph based on results similar to those of
A process for recovering aluminum from fly ash and 50 FIG. 8 in which percent volatilization of alumina and
other materials containing iron and silicon by the chlori- iron are plotted against each other at temperatures
nation route which compri~ first separating iron from varying between about 800' C. and 1050' C.
the remaining metals by selectively chlorinating the FIG. 11 is a graph based on results similar to those for
iron in an oxidizing atmosphere (about 5 to 100 percent FIG. 10 in which percent silica and alumina volatilized
added oxygen by volume) and vaporizing it followed by S5 are plotted against each other.
chlorinating the residue containing the remaining metals
including aluminum, silicon, titanium, alkali and
alkaline earth metals, and some iron, in a reducing atmosphere
of carbon monoxide in the absence of solid carbon
to suppress the chlorination of silicon, vaporizing 60
the chlorides of aluminum, silicon, titanium and the
remaining iron, separating a recovering the vaporized
chlorides by selective condensation, and treating the
fmal residue with sulfuric acid to convert calcium chloride
to disposable gypsum with simultaneous regenera- 65
tion of a dilute HCI solution for purposes of prechloridizing
the fly ash feed and also providing a suitable
binder for pelletizing the fly ash feed.
Conditions
IFeed: 20 g. BCI-bound pellets, minus 1/4" + 6-mesh.
2Feed: 30 g. BCI-bound pellets rather than 20 g.CI2I02 ratio, 2/1 instead of 1/1 as 60
in other tests.
3Feed: 20 g of BCI-bound pellets prepared from minus 32S-mesh ground fly ash.
The table shows that hydrochloric acid bound pellets
were satisfactory for volatilizing. iron and very little
aluminum, silicon and titanium, particularly at tempera- 65
tures between 800· C. and 1050· C. In addition to showing
the effectiveness of the chloridizing pelletization,
the results also show the effect of temperature on the
4,159,310
3 4
Periodically the collected dry fly ash is transferred to oxidizing chlorination, and indicate that either a higher
a dry storage hopper. temperature, perhaps 1150· C., or a longer reaction time
The dry fly ash can be sent to a dry magnetic separa- would produce a fly ash residue pellet almost totally
tion step. Optionally, in this step 50-60 percent of mag- free ofiron, that is, over 99 percent removal, with virtunetite
iron can be removed by magnetic separation. S ally no loss of aluminum values or excessive chlorine
The fly ash is next sent to the pelletizing step where consumed in volatilizing silica.
a·hydrochloric acid binder solution is added and it is Both hydrochloric acid and sulfuric acid·are suitable
pelletized into high-density, high strength pellets in binders· for carbon-free pellet compositions. Fly ash
conventional equipment such as a California Pellet Mill without any binder produces a weak pellet when sinpelletizer.
Following pelletizing, the pellets are dried at 10 tered at 300· C. The presence of carbonaceous material
about 300· C. in a direct ftred tunnel dryer. Dry pellets al h
are inventoried for feed to the shaft chlorinator or fur- so reduces the pellet strengt .
The pellets are dried with fuel-air or by recuperation
nace. The fly ash may be ground before pelletizing; of heat from high temperature gases exiting the oxidahowever,
it was found that this does not affect the recovery
ofthe metal values. Pelletizing is mandatory for 15 tion chlorinator and stored pursuant to chlorination.
a shaft reactor. Sequential chlorination techniques are As seen from the flow sheet of FIG. 1, the oxidative
amenable to the plug-flow nature of the shaft chlorina- chlorination step comes next followed by reductive
tor. chlorination. It was found that the most effective proce-
Various binders were tested for the pellets, for exam- dure was to ftrst remove the iron by selective chlorinapIe,
sulfuric acid, hydrochloric acid, and sodium chlo- 20 tion in an oxidative chlorination step followed by volaride.
Bentonite was tested to see if the hot strength of tilization of the formed ferric chloride and its recovery
the pellets could be improved. The latter produces a by condensation. Up to 98 percent of the iron was volastronger
pellet if the sinteringis done at 1000· C. Shaft tilized with substantially no chlorination or volatilizachlorinations
require a high-crush, strong pellet feed tion of the other metal values. It is important, of course,
which does not lose strength during chlorination. 25 that substantially no aluminum chloride be formed or
Carbon-containing pellets were not satisfactory. volatilized at this stage. As one of the big economic
Testing showed that they lose most of their strength factors involved with the process is the uSe of chlorine,
during chlorination while carbon-free pellets appeared it is also important to suppress the chlorination of the
to maintain their integrity throughout the chlorination other metal values, particularly silicon, as the fly ash
and the residue pellets are about as strong as feed pel- 30 contains over 25 percent silicon.
lets. As will be borne out later,solid carbon was not It was found that the degree of silica chlorination in
satisfactory as a reducing agent for the reductive chlori- the reductive chlorination step can be greatly reduced
nation. Extrusion or compaction-type pelletizers Were by using only carbon monoxide as a reducing agent
found to be the most satisfactory for low-density fly ash rather than a mixture of carbonaceous matericl and fly
materials. Pellets bound with hydrochloric acid provide 35 ash. Carbon monoxide improves the selectivity of aluto
be the most satisfactory although sulfuric acid is a mina chlorination over that of silica. The injection of
suitable binding agent. As will be seen from the flow silicon tetrachloride into the reaction gas mixture of
Sheet, liquid from the sulfuric acid treatment ofthe fmal chlorine and carbon monoxide was found to be very
residue was recycled to the pelletizing step and this effective in almost completely eliminating silica chloriliquid
containing hydrochloric acid and some small 40 nation at 950· C., for example.
amounts of metal chlorides ueas found to be a satisfac- It was found that the overall chlorination procedure
tory binder for the pellets. The data in the following resulted in chlorination of alkali and alkaline earth met-
Table 1 was obtained in oxidizing chlorinations of hy- als present. Suppression of the chlorination of these
drochloric acid bound pellets. elements which end up in the fmal residue as chlorides
_________T;;.a;;"b;,;;l..;,e_I 45 was not emphasized because a feasible way of disposing
Oxidizing Chlorinations of Pelletized Fly Ash Feed of the chlorides in the residue was found. It was found,
CI2 100 cc/min however, that the best reaction conditions for minimiz-
Atmosphere: 02 100 cc/min ing chlorination of sodium and magnesium was the
_____~Te::::m::lpe=ra:::tu:::;re"'"lT..:..::im:::e:.:.A.:s=-=in=:di=ca=ted=-__--:--:::-__- 50 absence of carbon during the chlorination and chlorina-
Test Temp. Time, CI2 Stoichio- % Volatilization tion at a temperature of about 950· C.
No. ·C. min. metry for Fe Fe AI Si Ti The oxidative chlorination for the selective removal
11 600 40 10.3 13.8 0 0 of iron is preferably performed on fly ash pellets with a
~: ~~ ::: :g:~ ~i:~ g g hydrochloric acid binder in a shaft chlorinator. At-
41 950 40 10.3 90.1 0 0 55 tempts to remove iron from the pellets by perchlorina-
51 800 120 30.9 69.0 1.6 0 tion under reducing or neutral conditions were not
~ 950 40 10.1 90.9 3.6 3.6 feasible because of co-chlorination ofexcessive amounts
73 950 30 6.0 83.0 0 0
81 1050 58 9.9 95.6 l.l 0 0 of alumina.
A number of shaft furnace chlorinators used as batch
chlorinators is preferred. These chlorinators are operated
with staggered sequence of operation designed for
optimum heat recuperation. For the oxidation chlorination,
the charge is brought up to the proper temperature
with hot, neutral combustion gases from a coal-fired
furnace. A mixture of chlorine and oxygen gases is then
circulated for about three hours through the charge to
prechlorinate and volatilize about 90 to 95 percent of
iron content. The volatilized ferric chloride is collected
6
TABLE 3-continued
Element %
MgO 0.002
Na20 0.40
TiOz 0.005
K20 0.005
Pzos 0.005
4,159,310
5
in an air-cooled scraped condenser. The next step is the
reductive chlorination.
Carbon monoxide gas is added to the chlorinator.
The reaction with carbon monoxide is sufficiently exothermic
to be self-heating. The chlorinator is operated 5
for about four to eight hours to collect a small amount
of residual iron chloride in the first stage condenser and
a high purity aluminum chloride in the second stage
condenser. About three percent silicon chloride by Optimum chlorination conditions of temperature,
volume is injected during the reduction to suppress 10 reaction time, and level of silicon tetrachloride were
silica chlorination. A third-stage condenser collects the established for the reducing chlorinator. A silicon tetrachlorides
of titanium and silicon. The on-stream chlo- chloride concentration in the chlorinator feed gas of
rinator is then purged with ambient air to remove resid- three percent and a temperature of 1050· C. reduced
ual chlorine and cool the residue. The purged gas is silica chlorination to about three percent while still
routed to a chlorinator coming on line for heat up and 15 sustaining an alumina recovery of nearly 80 percent.
to react with the residual chlorine and silicon chloride. Iron is controlled by selective oxidation prechlorination
A preferred method of introducing the silicon chloride and also by further purification of the off gas using
is to run the chlorine through the liquid silicon chloride fractional condensing at two temperature levels. Silica,
before it enters the reactor. The cooled depleted pellets potentially a large consumer of chlorine, is almost comare
conveyed to the leach circuit where water soluble 20 pletely rejected by use of carbon monoxide only as a
chlorides are removed and calcium is converted to reductant, that is, no solid carbonaceous additive, and
gypsum with sulfuric acid. The residue solids are ftI- by the injection of small quantities of silicon tetrachlotered,
washed and sent to the disposal while the hydro- ride in the feed gas. The residue treatment, which will
chloric acid solution is evaporated as required for water be outlined below, provides a method for dealing with
balance control and recycled to the pelletization step 25 alkali metal and alkaline earth metals;
for reuse as pellet binder and perchloridizer. Oxidation chlorinations were performed on a number
Analyses of metal volatilizations set forth in the tables of samples of fly ash briquettes bound with hydrogen
below were determined from feed and residue analyses. chloride binder and the results are presented in the
Analysis of a typical fly ash used in the examples set following Table 4.
TABLE 4
Chlorination Conditions
Chlorine Carbon Monoxide Results
Stoich. Stoich. Oxygen SiC4 CIZ
Test Wt. Flow for Flow for Flow Flow Vol. Temp. Time Efficiency % Volatilized
No. g cc. min Element cc/min AI cc/min cc/min % ·C. min. Cumu. Al Si Fe Ti
I. 20 100 1O.I·Fe 100 950 40 5.2 ",() -0 90.1
2 20 100 1O.I·Fe 33 950 40 <20 3.6 3.6 90.9
3 30 100 6.O-Fe 100 950 30 (-2.8) ",() ",,0 83.0
4 30 100 9.9·Fe 100 1050 58 4.3 1.1 ",() 95.6 ",,0
Element %
65
Al 99.426
SiOz 0.025
FeZ03 0.Q3
Cao 0.06
55
From the above results it will be seen that about 90 to
96 percent of iron was volatilization of 1 to 3.6 percent
aluminum, 0 to 3.6 silicon, and no titanium. A mixture of
45 chlorine and oxygen was used as the chlorinating gas
mixture. The oxygen oxidizes the silicon to silicon dioxide
and suppresses its chlorination. This also happens in
the case of aluminum and titanium.
FIG. 2 shows the effect oftemperature on the percent
50 of iron volatilized in accordance with the oxidizing
chlorination step. It will be noted that at 1050· C. about
95 percent of the iron is recovered, indicating that a
total recovery could be obtained at higher temperatures
probably in the neighborhood of 1100· to 1200· C.
FIG. 3 shows the percent of iron, aluminum and
silicon volatilized in the oxidative chlorination step at
various chlorine stoichiometries (X for Fe). Since the
process recycles the chlorination off gas, the stoichiometry
figures in the laboratory investigation are indicative
only of the relative rates of chlorination in a short
depth of pellets. Full scale chlorinator operation using
recycle techniques can attain complete utilization of
chlorine. The temperatures were below 800· C. It will
be noted that practically no silicon or aluminum are
volatilized in the procedure.
FIGS. 4 and 5 are descriptive of the degree of chlorination
of aluminum, silica and iron at various temperatures
and amounts of chlorine added. These results are
14.0
25.4
2.69
1.02
4.31
1.06
0.670
0.491
0.116
0.34
0.053
0.0006
0.008
13.9
25.5
2.72
1.03
4.66
1.05
0.694
0.581
0.182
1.56
0.072
0.0009
0.009
TABLE 3
Characterizing Fly Ash and Bottom Ash Feeds
Element Fly Ash, % Bottom Ash, %
Al
Si
Fe
Ti
Ca
Na
K
Mg
S (Total)
C
PzOs
U
V
In order to illustrate the objectives ofthe process, the
reported purity requirements for an al.uminum chloride 60
feed material to an Alcoa-type alummum cell are reported
in Table 3.
forth herein is as follows:
TABLE 2
4,159,310
8
It can be seen from the above results that from about
54 to about 77 percent of the aluminum, from 0 to 4.7
percent silicon, and from about 50 to about 100 percent
of iron was recovered. The results illustrate the effec5
tiveness of the process for recovering substantial percentages
ofaluminum and residual iron by the reductive
chlorination step, with chlorination of silicon and titanium
being effectively suppressed.
A number of tests were made to compare the effec10
tiveness of solid carbon and carbon monoxide as reducing
agents in the reductive chlorination step. The results
of these tests are presented in the following Table 6.
The results are also comparative to the use and non-use
of silicon chloride as a suppressant for the chlorination
of silicon. The samples had fll'st been subjected to the
oxidative chlorination step.
TABLE 5
7
based on tests involving neutral chlorinations, that is,
neither oxidative or reductive. When the results of
Table 4 are compared with these results, the effectiveness
of oxidative chlorination in suppressing the chlorination
ofaluminum and silicon is graphically illustrated.
A number of tests using the reductive chlorination
procedure described above were run on samples, one of
which (Test 4) had already been subjected to oxidative
chlorination, and the results are set forth in Table 5
below. Carbon monoxide was used as the sole reducing
agent and it was introduced as a mixture ofchlorine and
carbon monoxide. The chlorine was fll'st bubbled
through liquid silicon tetrachloride which was introduced
in this manner to suppress the chlorination of
silicon. 15
Chlorination Conditions
Chlorine Carbon Monoxide Results
Stoich. Stoich. Oxygen SiCk CI2
Test Wt. Flow for Flow for Flow Flow Vol. Temp. Time Efficiency % Volatilized
No. g cc.min Element cc/min AI cc/min cc/min % ·C. min. Cumu. AI Si Fe Ti
I 30 220 13.Q-AI 100 5.0 ",,14 ",,4.2 950 360 <9.8 55.6 ..0 89.7
2 30 220 13.Q-AI 100 5.9 ",,24 ",,6.9 950 360 <13.5 53.8 ..0 97.0
3 30 220 13.Q-AI 100 5.9 ",,2) ",,6.1 1050 360 <15.3 70J 0.0 10.
4 25.3 220 13.5-AI 100 6.1 ",,22 ",,6.4 1050 360 20-30 71.5 ..0 49.4
5 30 220 13. I-AI 100 6.0 9 2.6 1050 360 77.2 4.7 95.5
30
35
40
45
50
55
60
65
TABLE 6 EXAMPLES
A chlorine flow rate of 220 cc/min and a carbon monoxide flow rate of 100 cc/min was used in all of the above examples.
Solids Charge
Fly ash Carbon
Wt. Wt.
g g Stoich.
30 6
33 6
.!'"
U.
\0
W-o
'0
... Q
0.6
0.6
0.4
0.7
Ti
0.5
0.3
6.8 20.9
Chlorination
Residue
5.9 30.8 0.56
8.8 27.9 0.11
Assay %
8.1 30.2 0.18
3.7 23.4 0.12
9.7 29.7 0.34
2.8 33.1 0.00
9.0 30.3 0.28
6.5 27.1 0.16
4.8 27.6 0.08
5.8 30.3 0.54
7.3 22.4 0.34
7.9 23.8 0.37
8.5 24.1 0.40
7.0 22.8 0.28
7.7 0.28 0.4
At Si Fe
12.1
22.5
19.7
16.0
21.2
22.9
9.1
20.1
19.0
Ti g
49.6 26.7
60.7 15.9
72 18.1
79.8 16.0
76.7 16.0
76.6 16.8
62.2 16.2
8.2 96.6
8.9 94.7
5.2 84.7
22.3 95.6
3.2 91.4
20.1 100.0
5.0 85.4
45.8 98.6
53.4 93.4
47.7 92.4
49.0 92.0
~.O 88.6
~64 ~98
~57 ~95
38.3
67.2
46.9
87.5
55.0
65.6
45.9
67.4
82.8
68.1
66.9
72.2
72.9 52.6 90.2
69.2 44.7 93.8
",74
",89
24
27
30
30
27
33.5
53.5
56.6
49
67
18-20
~31
~3O
ISO
ISO
ISO
300
300
300
157
300
300
300
ISO
ISO
124
1" ~
130 ~
ciency
Time % Cumu- % Volatization
min. lative At Si Fe
9SO
950 150
950
9SO
9SO
9SO
9SO
9SO
9SO
9SO
9SO
9SO
9SO
9SO
Temp
·C.
10SO
10SO
~14.5
~13
..19.5
~5.6
~13
SUmmary of Fly Ash Chlorinations
Results
CI2 Effi-
~8
SiC4
Flow Vol.
cc/min. %
",19
~8
",54
5.1 ",77
5.1
5.1
2.5
2.7
5.1
2.5
1.8
2.6
2.2
2.2
1.8
2.3
1.9
co
~5.7
~5.7
Stoich.
4.8
4.8
4.0
4.0
Chlorine
Conditions
6.0
5.6
5.7
5.6
5.0
4.2
C I2
11.2
11.2
11.2
12.5
11.2
Stoich.
~12.5
2.0
2.0
1.0
o
o
o
o
2.2
2.2
2.2
o
o
o
o
2.2
2.0
7.1
7.1
o
o
o
4.3
o
o
o
o
6
6
6
o
30.0
30.0
30.0
30.0
30.0
30.0
30.0
30.0
30.0
40.0
30
30
Type
15
13
12
11
8
9
Monmagnetic
Sulfatized
FA
F.A.
FA
Pugged FA
in CI,SO",H + 32
PACKED TUBE TESTS
6 HCI Pellets 40.5
lXCarbon
H2S04Pellets
No Carbon
HCI Pellets
No Carbon
HCI Pellets
No Carbon
10 HCL Pellets
No Carbon
FineHCL
Pellets
HCI+2xcarbon
Pellets
H2S04 Pellets
No Carbon
14 HCl Pellets
No Carbon
HCl Pellets,
No Carbon
16 HCl + 2x
Carbon Pellets
7
1
2
3.
4.
5.
Test
No.
4,159,310
11
Examples 1-6, 12 and 16, using either solid carbon
alone or a mixture of solid carbon and carbon monoxide
12
made are as follows: Percent volatilization at 950· C.
versus Ch Stoichiometry (for AI)
Volatilization, %
Example 5.6 X 'clz stoich. at 11.2 X Clz stoich.
No Type of Pellet Feed Al Si Fe . Al Si Fe
HCI Binder, no carbon, 46.4 3.4 91.9 65.6 22.3 95.6
plus 6-mesh
2 HCI Binder, no carbon, 55.0 8.9 94.7
minus 6-/plus 2Q-mesh
3 HZS04 Binder, no carbon 67.3 5.1 85.0
FIG. 6 is a graph based on some of the data in the 45
tables presented above. It shows the effect of chlorination
temperature on the volatilization of iron, aluminum
and silicon in the absence of solid carbon using carbon
monoxide as the reducing agent. The experiments were
performed in a six inch long packed column with fly ash 50
pellets using a hydrochloric acid binder with no carbon.
The graph also shows the effectiveness of carbon monoxide
in suppressing silicon chlorination even without
silicon chloride being present.
FIG. 7 shows the effect of the amount of silicon chlo- 55
ride added on the chlorination of aluminum at temperatures
of 950· C. and 1050· C. Use ofsilicon tetrachloride
in more than five volume percent would be very effective
in suppressing the chlorination of silicon but substantially
reduces the chlorination of aluminum. 60
FIG. 8 shows the effect of the amounts of silicon
tetrachloride under 3-7 volume percent in suppressing
the chlorination of aluminum and silicon at. various
temperatures.
FIG. 9 shows the effect on the percent iron, .alumi-65
num and silicon volatilized at various chlorine stoichiometries
for aluminum at 950· C. Various conditions of
the test to obtain the results from which the graph was
30
67
o3
4-6
70-80
0-50
5-9
80
o
50
50
o
1.0
<1.0
90-96
oo
Process
Temperature
Gas composition:
CO, % (vol)
Clz,%
Oz,%
SiC4, %
Reaction time, hr.
Al recovery, %
Fe recovery, %
Si recovery, %
Ti recovery, %
FIGS. 10 and 11 are graphs based on a summary of
as a reductant, show that silicon volatilization is not 15 the results of tests of the process set forth in the tables
suppressed and that silicon is volatilized in amounts and other tests and they show in FIG. to the percent of
varying from about 45 to 64 percent. Examples 3 and 4 alumina volatilized against the percent of iron volatilshow
that the addition of silicon tetrachloride when ized and in FIG. 11 the percent of aluminum volatilized
solid carbonaceous materials are present has very little against the percent of silicon volatilized. Tests were
effect on the suppression of the chlorination of silicon. 20 made at various temperatures and show that there is
Examples 7, 8, 9, 10, 11 and 13 show that the use of some enrichment· or improvement in the ratio of alucarbon
monoxide alone is quite effective in suppressing mina chlorination' to either iron or silicon over the
the chlorination ofsilicon. Examples 14 and 15 show the range of alumina recovery but not to the degree that it
effectiveness of the addition of silicon tetrachloride on could be used as a purification technique.
the suppression of the chlorination of silicon. 25'The carbon monoxide used can be regenerated using
As the results of Table 6 show, suppression of the a hot coke bed such as a Wellman-Galusha carbon monchlorination
of silica was almost complete. oxide generator. Oxygen is added to maintain coke bed
Table 7 below provides a general summary of the temperature at 950· C. Oxygen is preferable to air to
results obtained by the overall process. avoid nitrogen buildup in the recycle gas. Alternatively,
TABLE 7 30 the recycled gas can be used as fuel either in pellet
--------...;;.~;..;;;;.---------- drying or the chlorinator preheat zone before going to
Stage I Stage II the carbon monoxide generator. .
~~~e::v~eChIOrination ~~:~~ion Chlorine utilization is related to the rate of gas flow,
or space velocity, with respect to bed volume. The·
950'-1050' C. 1050' C. 35 conditions obtained in the laboratory reactor are not
indicative of those which would be determined in a
pilot plant. The reaction rate appears to be proportionate
to bed temperature with a lesser dependence on
chlorine-carbon monoxide ratio in the reaction gas. The
40 preferred temperature range for the oxidative chlorination
step is from about 500· C. to 1200· C. and the same
for the reductive chlorination step.
It is seen from the above description of the invention
that reductive chlorination using only carbon monoxide,
that is, no solid carbonaceous additives such as coal,
coke, fuel oil, or pitch results in a large improvement in
rejection of silica chlorination with no loss in alumina
recovery. Eliminating solid carbonaceous materials as a
reductant has other advantages, such as, permitting
initial oxidation chlorination of the pellet charge, increasing
the strength of the pellets charged to the chlorinator
as there is no loss in pellet strength during the
chlorination as there is when coke, pitch or other carbonaceous
material is added. The combination of a small
quantity of silicon tetrachloride in the chlorination gas,
for example, three percent combined with carbon monoxide,
almost completely rejects silica chlorination with
only a small loss in alumina recovery. Ordinarily, an
oxidative chlorination followed by reductive chlorination
would necessitate an intermediate addition of coke
to the feed, which would be an expensive process step.
Surprisingly, this was found not to be necessary in this
process.
The .volatilized ¢hlorides are recovered by fractional
condensation. Off-gases containing volatile chlorides
are fractionally condensed at three temperature levels
to produce an iron chloride product, an aluminum chloride
fraction,. and a liquid mixture of silicon tetrachloTABLE
8
It is seen from the above description that an effective
and economical process has been provided for recover-
4,159,310
13 14
ride and titanium tetrachloride. Ideally, FeCl), AICl), sary. Silica chlorination is reduced by the process to a
SiCl4 and TiCl4 can be separated according to their level where all of the SiCl4 produced can be marketed.
relative volatilities in a series of cool condensers with As stated above, the chlorinations result in substanhigh
boilers condensing fIrst. Scraped condensers in tially all of the alkali metal and alkaline earth metals
two stages collect the crude FeCl4 and AICl) fractions. 5 being completely chlorinated and these must be dis-
A third stage condenser is chilled with a Freon refriger- posed of either by reuse or otherwise. It was found that
ation unit to condense SiC4 and TiCI4. A typical test substantially all of the calcium chloride is converted to
run without the oxidative chlorination step showed that gypsum by treatment with sulfuric acid as shown in the
two transition condensing stages produced a crude fer- flow sheet. The residue from the chlorination steps is
ric chloride containing 60 percent FeCl) and 40 percent 10 leached with dilute sulfuric acid (possibly from a S02
AICh at 170· C., and the third and fourth zone con- scrub-regeneration system on the power plant stack
denser stages produced a crude aluminum chloride of gas). This precipitates the calcium as gypsum, leaches
about 93 percent AICl) and seven percent FeCl). Both out water soluble chlorides (and a small amount of acid
SiC4and TiC4passed through the heated zones and are soluble chlorides) to produce an inert refuse suitable for
condensed at about _20· to -30' C. The quantative 15 disposal to existing ash ponds. The leach solution conanalyses
to determine the recoveries set forth in the tains dilute HCI, some residual H2S04 and a very small
tables above were made on the condensed products. amount ofalkali metal chloride. This solution is concen-
Chlorides of iron, aluminum, silica, and titanium leave trated by evaporation and sent to the pelletizing step as
the chlorinator along with unreacted carbon monoxide, shown to pelletize incoming fly ash feed. A further
chlorine and carbon dioxide, along with a small amount 20 result of the treatment is to pre-chloridize the alkaline
of particulate carryover. Staged condensing, whereby constituents of the fly ash, mostly calcium, and thereby
the volatile chlorides are successively removed is the reduce chlorine consumption by calcium remaining in
best approach for selective recovery. Unreacted chlo- the pellets. A weak HCI solution is regenerated by the
rine, carbon monoxide and carbon dioxide are recycled treatment of sulfuric acid with soluble calcium chloride
back to the chlorinator or CO regenerator. 25 to precipitate gypsum. The formed hydrochloric acid
Volatile chlorides are condensed in three stages. In prechloridizes the chlorine consuming alkaline earth
the fIrst stage a 220· C. scraped air condenser is used to metals using, indirectly, inexpensive sulfuric acid,
remove most of the ferric chloride. This product may thereby reducing chlorine consumption in the process.
Pellets prepared using the weak recycled HCI solution
be contaminated with cocondensed AICl), but the fmal 30 and chlorinated at typical conditions resulted in extracproduct
is marketable as a coagulant in tertiary sewage ti imil t th . dil t HCI
treatment, for example. A second stage condenser oper- b~:rs Th
ar ~ ~se u:~ u ed reage;tt f asha
ates at 90' C. with cooling water to condense all of the hl'·' e a .ve ~n . proce ~e o. rea mg ~ ~
AICI hi h' tamin d 'th . F CI F CI . c ormation residue WIth dilute sulfunc aCid to preclpl-
3w c IS con . ~te .WI som: e 3· e. 318 tate gypsum, using the ftltrate as a fly ash binder to
remove~ by pressure dlstillatlo~ at 250 C. ~o provl~e a 35 make pellets, and subjecting the pellets to chlorination
substantially pure ~C13 meetmg. the punty reqUIre- was tested and the results recorded in Table 8 below.
ments for commercial sale. A third stage condenser
operates at - 20· C. for near-complete removal of SiC4
and TiCl4 from the gas stream before recycle. Liquid A. H2S04 Leach of a Chlorination Residue
SiC4 and TiC4 are condensed and then separated by 40 Feed 16.0 g chlorination residue
fractional distillation. H20 16 m1 (50% solids) .
Non-condenS'lbIes tirom the third stage condenser THe2mperature SO' C. S04 ± 4.4 g H2S04(required for con.
consist of chlorine, carbon monoxide and carbon diox- verting all Ca + Mg to S04)
ide, and possibly some low-boiling trace chlorides. This Final pH 0.7, also H20 was added to make a
gas can either be burned for its heating value if the CO 45 stirrable slurry of the pasty
. hi h h 'f h . al hl mass formed when adding H2S04·
content IS g enoug and 1 t e resldu c orine is Approximate Extractions by Dilute H2S04 Leaching with
low, or it can be recycled back to the chlorinator. Car- the Precipitation of GyPSum.
bon monoxide and carbon dioxide can be recycled to Element Extraction, % gil in PF
the carbon monoxide generator. AI I.S 0.326
The preheat combustion chamber for preheating the 50 Si D.S 0.2S6
shaft reactor for both oxidative chlorination and reduc- Ca 11 2.14
tive chlorination is supplied with fuel and air for heat- ~: ii's g:~~
ing. As seen from the flow sheet, excess heat from the C1- 2S.8
chlorination steps is sent to the pellet drying step. The S04 33.8
utilization of all excess heat in the process contributes to 55 B. Pelletizing Fresh Fly Ash with Solution from A.
the latter's economic feasibility. ~~solution ~g :Ufly
ash
The low-iron, AICl3 product may be further purilled Procedure Slurry and dry overnight at 90' C.
by pressure distillation. The chlorides of silicon and Dry weight 32 g
titanium can be separated with high purity by fractional C. Chlorination of the Pelletized Fly Ash Feed
distillation. The SiCl4 is a saleable product. SiCl4 can be 60 Element. % Volatilization
recycled to the chlorinator to act as a chlorinating agent ASiI 72.2 S3.4
and suppress chlorination of more silica, packaged as a Fe ::::93.4
saleable liquid, or burned with oxygen to produce silica Ca 70
fume which is a saleable product and thereby regenerat- Mg 2S
ing chlorine for recycle. Actually, the combined steps 65 .N;..a;;...._.-;.II;;.... _
of prechlorination of iron and fractional condensing of
the AICl) and FeCh in the reducing chlorination will
probably make an aluminum purifIcation step unneces4,159,310
10
15
ing substantially pure aluminum, as well as other metal,
values, from fly ash by the selective chlorination and
condensing procedure outlined above and shown in the
flow sheet of FIG. 1. The process additionally provides
a means for disposing of the alkali metal and alkaline 5
earth chlorides in the residue with regeneration of hydrochloric
acid which can be reused in the process. A
maximum use of by-products and excess heat energy is
achieved by the process of the invention.
What is claimed is:
1. A process for recovering aluminum from fly ash
containing aluminum, iron and (silica) silicon which
comprises:
(a) chlorinating the material by subjecting it to the 15
action of chlorine at a temperature of about 500·
C.-1200· C. in an oxidizing atmosphere in the presence
of added oxygen in an amount equal to about
5-100 volume percent of the chlorine to selectively
vaporize iron as iron chloride; 20
(b) chlorinating the residue from step (a) by subjecting
it to the action of chlorine at a temperature of
about 500· C.-1200· C. in a reducing atmosphere in
the absence of solid carbon to vaporize the chlorides
of aluminum (tatanium) and silicon; and 25
(c) separating and recovering the formed (reacted)
chlorides from the vapors by selective condensing.
2. The process of claim 1 in which the reductive
chlorination of step (b) is performed in the presence of 30
carbon monoxide as a reducing agent.
3. The process of claim 2 in which silicon tetrachloride
is added to the residue from step (a) in an amount
up to about 19.5 volume percent to suppress the chlorination
of silicon. 35
4. The process of claim 3 in which the silicon tetrachloride
is mixed with chlorine used as the chlorinating
agent.
5. The process of claim 3 in which the reductive
chlorination of step (b) is performed at about 1050· C. in 40
16
the presence of silicon tetrachloride at a concentration
of about 3 volume percent.
6. The process of claim 1 wherein the fly ash contains
calcium and in which the material (residue of solid
chlorides) from step (b) remaining after vaporization is
reacted with sulfuric acid to produce disposable gypsum.
7. The process of claim 1 in which chlorine and oxygen
are mixed for the chlorination of step (a).
8. The process of claim 1 in which the reductive
chlorination of step (b) is performed in the presence of
carbon monoxide as a reducing agent.
9. The process of claim 8 in which the carbon monoxide
is introduced at a volume percent of about 20 percent
to about 80 percent.
10. The process of claim 8 in which silicon tetrachloride
is added to the residue from step (a) in an amount
upto about 19.5 volume percent tei suppress the chlorination
of silicon.
11. The process of 10 in which the silicon tetrachloride
is mixed with chlorine used as the chlorinating
agent.
12. The process of claim 11 in which the silicon tetrachloride
is introduced in an amount of about 2.5 to
about 19.5 volume percent.
13. The process of claim 1 wherein the fly ash contains
calcium and in which the material (residue ofsolid
chlorides) from step (b) remaining after vaporization is
reacted with sulfuric acid to produce disposable gypsum
and to form hydrochloric acid.
14. The process of claim 13 in which the fly ash feed
is pelletized.
15. The process of claim 14 in which the fly ash feed
is pelletized and bentonite is used as a binder for the
pellets.
16. The process of claim 1 in which titanium is present
in said fly ash and it is chlorinated in accordance
with step (b) and separated and recovered in accordance
with step (c).
* * * * *
45
50
55
60
65
UNITED STATES PATENT OFFICE
CERTIFICATE OF CORRECTION
Patent No. 4,159,310 Dated June 26, 1979
Inventor(s) JAMES E. REYNOLDS, ET AL.
It is certified that error appears in the above-identified patent
and that said Letters Patent are hereby corrected as shown below:
Claim 1: Column 15, line 12, delete" (silica)".
Claim 1: Column 15, line 25, delete II (tatanium)".
Claim 1: Column 15, line 26, delete "(reacted)".
Claim 6: Column 16, lines 4 and 5, delete "(residue of
solid chlorides)".
Claim 13: Column 16, lines 27 and 28, delete" (residue
of solid chlorides)".
5igncd and 5caled this
Eighteenth Day 0 f Nm'ember J91W
ISEALI
..ftt~st:
SIDNEY A. DIAMOND
Att~st;"g Offic~r Comm;ss;o,,~r of Pllte"ts IIIId Trlldemarlu