4,159,310 Process for recovering aluminum and other metal values from fly ash

Patent Number/Link:

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

t }-"--I I

OXIDATIVE I--------~-.J r-- REDUCTIVE

CHLORINATION CHLORINATION

(BATCH) (BATCH) ..

eyE L--_ 12 J I 1 H2SO4

1 1i

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------------------.

Cl 80

!::! 70

!;(

..J 60

~ 50

~ 40

..J

UJ 30

lL o'*' 20

500!=--~'!::-=----=:±-=---~~'--~~--=":=-'",."

FIG 2

o 70r--------::::::::::::='\O

!:::! 60

:'"5"" 50

Iz- 40

:E 30

..J

UJ 20

o 10

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)

..... Fe

0 80

::J • 750·C

~ / 0

...J ..... AI

::E

...J

I.L. 60

0 /

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

I- 60 «

::J

I«- 50

...J

>40

700

100

G ----0Si

800 900 1000 \lao

CHLORINATION TEMP. °c

FIG 6

9:x: u

~30

Si, 950 AND 10500 C

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

Ol--__~-_o-..."._I_-_o____:...J--_o____,..J

700 1100

!;(

a: 60

::I: o

I- 50

~ 40

-w'

#.30

FIG 8

u.s. Patent Jun. 26, 1979 Sheet 7 of 8 4,159,310

100 ....-----r---,r---r---,--.,----,---.,----,--.----,--,-----,

Fe(2)@--_-- ~I)

0Fe(3)

...J

!< 60 ...J o>

I- 50

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 .

O~_I-----JL..------.A..,--..I..:----=,"=:----=l:---:::f-=---=-=-~

o 10

~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

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

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

TABLE 3-continued

Element %

MgO 0.002

Na20 0.40

TiOz 0.005

K20 0.005

Pzos 0.005

4,159,310

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 %

Al 99.426

SiOz 0.025

FeZ03 0.Q3

Cao 0.06

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, %

S (Total)

PzOs

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

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

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

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

.!'"

W-o

... Q

0.6

0.4

0.7

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

33.5

53.5

56.6

18-20

~31

~3O

ISO

300

157

300

ISO

124

1" ~

130 ~

ciency

Time % Cumu- % Volatization

min. lative At Si Fe

9SO

950 150

950

9SO

Temp

·C.

10SO

~14.5

~13

..19.5

~5.6

~13

SUmmary of Fly Ash Chlorinations

Results

CI2 Effi-

SiC4

Flow Vol.

cc/min. %

",19

",54

5.1 ",77

5.1

2.5

2.7

5.1

2.5

1.8

2.6

2.2

1.8

2.3

1.9

~5.7

Stoich.

4.8

4.0

Chlorine

Conditions

6.0

5.6

5.7

5.6

5.0

4.2

C I2

11.2

12.5

11.2

Stoich.

~12.5

2.0

1.0

2.2

2.0

7.1

4.3

30.0

40.0

Type

Monmagnetic

Sulfatized

F.A.

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

Test

No.

4,159,310

Examples 1-6, 12 and 16, using either solid carbon

alone or a mixture of solid carbon and carbon monoxide

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

4-6

70-80

0-50

5-9

1.0

<1.0

90-96

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

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

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

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

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).

* * * * *

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