United States Patent [19]
Reynolds
[11]
[45]
4,108,635
Aug. 22, 1978
3,160,352
3,675,859
3,754,897
3,770,424
3,892,563
3,905,808
[54] SOLDER SKIMMINGS RECOVERY
PROCESS
6 Claims, 1 Drawing Figure
FOREIGN PATENT DOCUMENTS
757,426 9/1956 United Kingdom 75/77
Primary Examiner-L. Dewayne Rutledge
Assistant Examiner-Michael L. Lewis
Attorney, Agent, or Firm-Sheridan, Ross, Fields &
McIntosh
[57] ABSTRACf
An improvement in the method for recovering marketable
values of solder, lead, and a zinc chlorideammonium
chloride solution from solder skimmings
which comprises grinding the skimmings, water leaching
the skimmings to dissolve the zinc chloride and
ammonium chloride, screening the leach residue to
recover solder from the leach slurry, separating the
ammonium and zinc chloride solutions from the lead
chloride in the leach slurry, and contacting the lead
chloride with an alkaline flux, a reductant, and an oxygen-
containing gas under heat to recover lead from the
lead chloride.
Inventor: James E. Reynolds, Golden, Colo.
Assignee: Hazen Research Inc., Golden, Colo.
Appl. No.: 670,695
Filed: Mar. 26, 1976
Int. Cl.2 C22B 13/00; C22B 13/04;
COIC 1116; COlG 9/04
U.S. Cl 75/24; 23/267 R;
75/78; 75/97 A; 241/20; 423/98
Field of Search 75/77, 78, 79, 85, 97 R,
75/97 A,l20, 121, 24; 241119, 20, 24; 29/403;
228/34; 23/267 R; 423/98
References Cited
U.S. PATENT DOCUMENTS
12/1964 MoHring 23/267 R
7/1972 MitcheH 241/24
8/1973 Derham et al. 75/77
11/1973 Floyd et al. 75/24
7/1975 LaPoint 23/267 R
9/1975 Bzura 75/101 R
[56]
[75]
[73]
[21]
[22]
[51]
[52]
[58]
GRIND
SKIMMINGS
ROTARY DRUM 1-----1
WATER LEACH
WATER
WET SCREEN
8 MESH
FURNACE
400°C
ZnCla • X NH.CI
(X-2,30RG)
FOR SALE
OFF GAS
DRYER
REFINED
LOAD FOR SALE
SLAG
u.s. Patent Aug. 22, 1978 4,108,635
GRIND
SKIMMINGS
ROTARY DRUM
WATER LEACH WATER
Ir
WET SCREEN +8 FURNACE REFINED SOLDER
8 MESH MESH 400°C FOR SALE
MESH.....
r,WAsH
NH4C1
WATER
FI LTER
FILTRATE RATIO ADJUST - DRUM
ZnCI2 TANK DRYER
FILTER.....
NH4CI
+ H2O
CAKE
PbClz ZnCIz. • X NH4CI
GAN<!>UE -SODA ASH (x = 2,3 OR G)
WATER FOR SALE
SOLDER rCOAL (-100 MESH)
PELLETIZER
OFF GAS
~~
Ir
DRYER
FURNACE REFINED - 900°C - LOAD FOR SALE
•
-8
SLAG
SOLDER SKIMMINGS RECOVERY PROCESS
SUMMARY OF THE INVENTION
The invention is an improved process for recovering
values from solder skimmings which comprises grinding
the solidified skimmings, water leaching the ground
skimmings to dissolve zinc chloride and ammonium
chloride away from the pieces of occluded solder and
lead chloride, screening the residue from the water
leach to recover the pieces of solder from the lead chloride
(PbCI2), and the ammonium chloride and zinc chloride
solution, and contacting the lead chloride with an
alkaline flux, a reductant, and an oxygen-containing gas
(most preferably air) under heat to recover lead from
the lead chloride.
4,108,635
1
BACKGROUND OF THE INVENTION
2
found, however, that a water leach conducted in a pebble
mill-rotary drum provides the additional mechanical
attrition to liberate the metallic solder values. The solder
is sufficiently malleable to work free occluded parti-
5 cles of lead chloride and permit leaching out water
soluble zinc and ammonium chlorid,es. Solder pieces are
not reduced in size to any extent, and thus it is possible
to separate the values in the feed into three initial products
on the basis of the difference in particle size:
10 l. An aqueous solution of zinc chloride and ammonium
chloride.
2. Metallic nodules of solder.
3. A cake residue containing lead chloride and some
silica gangue.
15 The zinc chloride-ammonium chloride solution can
be marketed, without further processing, as an aqueous
preflux for continuous strip or wire galvanizing. If required
for marketing, the ratio of ammonium chloride
l. Field of the Invention to zinc chloride can be increased to mole ratios of either
The invention is in the field of recovery of values 20 2/1, 3/1, or 6/1, or whatever is required for sale, by
from scrap solder and solder skimmings. addition of ammonium chloride, then dried as a flake or
2. Description of the Prior Art granular product.
Solder baths used in can manufacturing are covered The metallic nodules of solder containing some residwith
a layer of ammonium chloride flux to prevent ua1lead chloride, primarily as a thin surface coating, are
oxidation of the solder. Zinc chloride is added to the 25 wet screened with a screen size to provide the cleanest
flux to reduce fuming of the molten ammonium chlo- separation of solder and lead chloride. A screen size of
ride. Lead oxide present reacts with the chlorides to 8 mesh has proved most effective. Solder nodules, anaform
lead chloride. In skimming off the slag which is lyzing about 85% Pb and 3% Sn, are refined by melting
formed as the cans are soldered some of the flux and in a furnace at 400· C. The slag is mostly lead chloride
solder is removed because of the inefficiency of the 30 which is raked off. It can be added to the residue cake
skimming procedure. The skimmings after they harden in the following step. The melting point of the solder is
contain solder chunks and granular lead chloride in a checked and the Pb-Sn ratio adjusted by minor addimatrix
of solid ammonium chloride and zinc chloride. tions of purchased tin or lead to meet marketing specifi-
These skimmings are referred to herein as solder skim- cations.
mings or solder bath skimmings. 35 The filter cake from the screening is mostly lead
The existing process for recovering solder from sol- chloride contaminated with silica and a small amount of
der bath skimmings consists ofmelting the skimmings in solder. Since there is little or no market for lead chloa
gas-fired furnace, tapping the molten solder and dis- ride, it is best to convert the lead chloride to lead by
carding the top layer of zinc chloride, ammonium chlo- reacting it with an alkaline flux, a reductant, and an
ride, and lead chloride. In the process of furnacing, an 40 oxygen containing gas in a furnace at a temperature
ammonium chloride fume is emitted from the stack at a preferably between about 750· C and 1100· C. Soda ash
level far in excess of current air pollution control limits. (Na2C03) has been found to be the most effective alka-
Air pollution correction equipment for the off-gas is line flux although other alkaline fluxing agents, such as
costly. High energy wet venturi scrubbers will not meet lime, can be used. Coal is the most effective reductant,
present air pollution codes on plume opacity. Electro- 45 and air the most effective oxygen containing gas. Many
static precipitators are prohibitively expensive since the carbonaceous materials such as fuel oil, coke, molasses,
elements must resist corrosive attack by the acidic or pitch may be substituted for coal. The result of this
fumes. reaction is the formation of a fluid NaCI top layer and a
In view of the disadvantages of prior processes for bottom layer of pure molten lead. The chemical equarecovering
solder from scrap solder skimmings, there is 50 tion for the reaction is:
a need for a method for economically and practically
recovering solder from the solder skimmings which is
within acceptable air pollution control limitations.
The following example is illustrative of the invention
but not limiting thereof.
EXAMPLE 1
One ton of a feed of solidified solder skimmings
60 ground to about 1-1 inch top size and containing by
weight percent 20% metallic solder, 47% zinc chloride,
13% ammonium chloride, 18% lead chloride and 2%
gangue was combined with 1120 pounds of water in a
rotary drum and leached for about 60 minutes under
agitation.
The leach slurry from the rotary drum was then
screened through an 8 mesh screen to recover solder
pieces from the leach slurry, yielding a +8 mesh prod-
DESCRIPTION OF THE PREFERRED
EMBODIMENTS
It has been discovered that a simple water leach, after
grinding the skimmings, will dissolve the zinc chloride
and ammonium chloride compounds away from the 65
pieces ofoccluded solder, providing the matrix is low in
lead chloride. Since lead chloride is essentially water
insoluble, it makes a water leach more difficult. It was
BRIEF DESCRIPTION OF THE DRAWING 55
The drawing is a flow sheet which illustrates the
complete process ofthe invention for recovering solder,
a solution of zinc chloride and ammonium chloride, and
lead from scrap solder skimmings.
4,108,635
3
uct containing 372 pounds of solder and 66 pounds of
lead chloride. The solder was melted in a furnace at
400· C with no visible emission of fumes and skimmed
to remove 70 pounds of slag, with 368 pounds of solder
remaining, a 92% recovery based on the solder in the 5
feed. The lead chloride can be sent to the subsequent
step for recovering lead from lead chloride.
The - 8 'mesh material was then filtered, with 90
pounds of water being used as wash water. A filtrate
weighing 2420 pounds and containing 930 pounds of 10
ZnC12,242 pounds of NH4Cl and 1210 pounds of water
was recovered and packaged for sale. This is a 97%
recovery of these two compounds based on their content
in the feed.
The filter cake, weighing 433 pounds and containing 15
284 pounds of lead chloride, 40 pounds of gangue, 81
pounds of water and 28 pounds of solder was then combined
with 130 pounds of soda ash (Na2COJ) and 30
pounds of -100 mesh coal and pelletized, resulting in
565 pounds ofgreen pellets. The pellets were dried with 20
75 pounds of water being evaporated, resulting in 490
pounds of dry pellets. These were heated to 900· C in a
furnace until the reaction was complete with the production
of 142 pounds of slag and a yield of 218 pounds
of lead, an 84% recovery based on the lead in the lead 25
chloride in the feed.
It is seen from the above results that the process is
essentially pollution free as all chlorides are recovered
as solutions and no gases are discharged into the atmosphere.
The high recovery from the solder skimmings 30
of all saleable materials of the required purity for marketing
demonstrates the economic feasibility of the
process.
What is claimed is:
1. A method for recovering solder, zinc chloride and 35
ammonium chloride, and lead from solidified solder
skimmings, comprising the following steps:
(a) grinding the skimming to a small size;
(b) water leaching the solder skimmings with violent
agitation to both mechanically separate and dis- 40
solve both zinc chloride and ammonium chloride
4
thereby freeing occluded pieces of solder and particles
of lead chloride;
(c) separating the pieces of solder from the leach
slurry;
(d) refining the reclaimed solder by heat to purify it;
(e) filtering the leach slurry to separate ammonium
chloride and zinc chloride solution and water from
the lead chloride;
(t) recovering a filter cake of predominantly lead
chloride; and
(g) recovering lead from the lead chloride.
2. The method of claim 1 in which in step (g) the lead
is recovered from the lead chloride by contacting the'
lead chloride with an alkaline flux, a reductant, and an
oxygen-containing gas.
3. The method of claim 1 in which in step (g), the lead
is recovered from the lead chloride by contacting the
lead with an alkaline flux, a reductant, and an oxygencontaining
gas at a temperature of from about 750· C to
about Iloo· C.
4. The method of claim 3 in which in step (c), the
pieces of solder are separated from the leach slurry by
screening the leach slurry through a screen having a
mesh size of about 8, lead chloride is recovered from the
molten solder in step (d) and added to the lead chloride
from which lead is recovered in step (g), the alkaline
flux is soda ash or lime, the reductant used in step (g) is
a carbon containing material, and the oxygen-containing
gas is air.
5. The method of claim 1 in which in step (c), the
pieces of solder are separated from the leach slurry by
screening the leach slurry through a screen having a
mesh size of about 8. .
6. A method for dissolving in water zinc chloride and
ammonium chloride from pieces of occluded solder and
granular lead chloride in solder skimmings which comprises
leaching said skimmings with water while violently
agitating the scrap solder skimmings in a pebble
mill-rotary drum to simultaneously mechanically separate
occluded solder and granular lead chloride.
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