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Патент USA US2111600

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March 22, 1938.
L.. D. MILLS ET AL
2,111,600
»PROCESS FOR RECOVERY OF PRECIOUS METALS
Filed June 2, 1936
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ATTORNEY
ïfatented Mar. 22, 1938I
2,111,600`
UNITED STATESVPATE
2,111,600
CIE
‘PROCESS FOR RECOVERY 0F PRECIOUS
METALS
Louis D. Mills> and Thomas B. Crowe, Palo Alto,
and Joyo C. Hann, San Francisco, Calif., as
siglnors to The Merrill Company, San-Francisco,
Calif., a corporation oi’ California
Application .lune 2, 1936, Serial No. 83,080
17 Claims. (Cl. 'l5-2)
This‘invention relates generally to metallurgi
um carbonate or other acid consuming sub
cal processes lused for the recovery of precious stances. If the solution of the pulp is to be
metal values from ores. As- disclosed herein they neutralized prior to precipitation, the presence
process utilizes both cyanldation and flotation
concentration operations.
of such substances in the >pulp necessitates a ma
terial increase in the amounts of reagents re-
`
Applicants have previously- devised a process> quired.
~
'
'making use of both cyanidation and notation
In general it is an object of the present inven
concentration operations, for the eñicient recov
tion to provide a combined cyanidation-iiotation
ery of precious metal values from ores. The process for the economical recovery of precious
10 process in that instance is characterized by ‘the
metal values from ores, Without neutralizing the
fact that precipitation is carried out in a- pulp solution of the pulp before precipitation.
consisting of comminutedore solids and cyanide
A further object of 'the invention is to provide
0
solution, as distinguished from> precipitating in ' a process involving precipitation oi' values in a
a clarified solution, as in conventional cyanida
pulp consisting of ore solids and cyanide solu
15 tion systems.
'The process also carries out pre.
cipitation While the solution of the pulp is sub
stantially neutral, and while it contains an acid
tion, which willenable economical treatment of
ores containing substantial amounts of -strong
oxidizing agents, like manganese dioxide, and/or
acid consuming agents, like alkali carbonate.
which 'serves to activate the zinc precipitant and
Another object of the invention is to provide
at the same time provides a reducing agent to
adequate 'treatment for preventing resolution
combine with and nullify the effect of oxygen , of values precipitated in an ore pulp, during a'
‘- _present >in the pulp. Such a'process is particu
subsequent flotation operation.
larly applicable to the treatment of gold ores
Briefly, the present process consists in con
where a cyanide solution can be employed, which tacting the comminutedore or tailings with al
25 after dissolving precious metal values from the
kaline'vcyanide solution to dissolve the readily
ore, does not contain suñicient cyanide in such soluble metals. Following this dissolution treat
condition as to properly activate zinc or a like ment, the pulp, that is, the mixture of finely
reducing` salt like sodium or calcium bisulphite, ,
metallic precipitant, for efticient precipitation.
divided oreA and solution, is conditioned for‘pre
- In many cyanidation system, the alkaline solu'e
cipitationby removing or inhibiting free oxygen
which may be present. This may be effected
by the introduction of a reducing agent such as
an alkali hydrosulphite, which will exist in an
alkaline cyanide solution, and which will com
30 tion employed may contain suiiicient cyanide to
properly activate a precipitant like zinc dust, for
eñicient precipitation of _the desired metal. The
term “alkaline solution” is here used _to desig
nate solutions or pulps which are alkaline to
35 phenol phthaline indicator, e. g. about pH 8.4.
When such conditions exist, it has been found
that precipitation in a combined cyanidation
flotation process such as described above, may
not require neutralization of alkalinity, together
with the presence of an activator, like an alkali
bisulphite,` for the precipitant. Furthermore sil
ver bearing ores, particularly if oxidized or part
ly oxidized, frequently contain appreciable
amounts of manganese dioxide, which is a strong
45 oxidizing agent and which rapidly attacks and
destroys salts like the alkali bisulphites. Thus in
a process in which such oxidizing agents are
present in a pulp, it maybe impractical to rely
bine with dissolved oxygen. . Since oxygen en
trained in the pulp ytends to go into solution, it
is likewise nullified by such treatment. Alter
natively, a major portion of the free oxygen may>
be removed by mechanical deaeratlon, after which
the remainder is combined With the chemical re
ducing agent as above described. The alkali 40
hydrosulphite serves not only to remove or in
hibit dissolved oxygen butmay also serve asv
a partial precipitant of the precious metals. The
oxygen free alkaline pulp is then completely
precipitated by the introduction of a suitable pre'
cipitant, such as zinc dust.
To accelerate and
render the precipitation more complete, a soluble
lead salt, such as lead nitratey may be added to
upon alkali bisulphite to condition the pulp for> ’ the pulp either prior to or'simultaneously With
50 eiiicient precipitation, because oxidation by man
the introduction of the zinc precipitant.y Both
ganese dioxide and like agents in the pulp, would the chemical deoxidation and the precipitation
are accompanied by vigorous mechanical agita
necessitate the use of relatively large' and waste
ful amounts of chemical.
tion under conditions which preclude re-absorp
In addition to the above, precious metal ores tion of atmosphere oxygen.
'
~
After precipitation is complete, the pulp is4
55 frequently contain substantial amounts of calci
2
2,111,600
conditioned for flotation by converting cyanogen
duction of a chemical deoxidizing agent, after
solvents present into compounds which are non
solvents for the precipitated metals. This can
-be accomplished by the addition of a suitable
salt of a heavy metal, such as copper sulphate.
The amount of copper `sulphate added is in ex
cess of that required to combine with cyanogen
solvents present. The stabilized pulp is then
which the dissolved precious metals can be rap- .
subjected to flotation for the recovery of the pre
such` as lead acetate or lead nitrate.
10 cipitated metals and any additional precious
metal bearing minerals which may be present.
Conventional flotation reagents may be employed,
as for instance suitable amounts of potassium
15
amyl xanthate, cresylic acid, and pine oil.
A representative embodiment of the present
process is shown in Fig. 1 of the accompanying
drawing. As indicated at I0, pulverized ore con
taining the precious metals to- be recovered, is
intermixed with alkaline cyanide solution and
20 subjected to agitation. During the course of this
treatment, the precious metal values which are
readily soluble, are extracted by the solution.
The pulp is then elevated by pump I2 to a closed
receiver II, the cylindrical portion of which is
25 ñlled with suitable grids over which the pulp
flows in thin films while subjected to a high vac
uum created by the vacuum pump I3. This treat
ment removes from the pulp substantially all of
the mechanically entrained air and also that dis
Deaerated
pulp leaves the receiver through main discharge
pipe I4, any excess being returned through over
flow pipe I5 to agitator I0, the amount returned
being controlled by regulation of pump I2. Re
35 ceiver II is provided with a steeply sloping coni
cal bottom I6, to prevent accumulation of solids.
Overflow pipe I5 extends below the pulp level in
agitator I0, and receiver I I is located at suilicient
height above the surface of the pulp in agitator
40 I0, to provide a barometric seal, preventing in
gress of air through overflow pipe I5, and al
lowing pulp to overflow freely from receiver II
into agitator I Il. This arrangement automatically
seals the`outlet of receiver II, and obviates the
30 solved in the solution of the pulp.
45 4use of an interior ñoat to ensure a constant pulp
level Within the receiver, which is necesary to pre
vent air from leaving the receiver through main
discharge pipe I4.
Mechanical deaeration equipment has hereto
50 fore been Widely used in conventional cyanidation
systems, to remove dissolved oxygen. from clari
iied solutions. An ore pulp may be similarly de
aerated, provided reasonable care is exercised in
maintaining movement of the pulp through the
55 evacuated deaerating receiver, to avoid clogging.
A pulp of this character contains both entrained
air particles and air dissolved in the solution, the
amount of entrained air tending to increase with
`an increase in viscosity or increase in the per
60 centage of slime particles, such as amorphous or
clay material. All of the free oxygen present, in
cluding both that contained in the mechanically
entrained air and that dissolved in the solution,
may be destroyed or its oxidizing eiîect inhibited,
65 by contactng the pulp with a chemical reducing
agent such as alkali hydrosulphite. However
where a considerable amount of total oxygen in
the pulp requires the use of relatively large
amounts of reducing agent to elïect its nulliilc'a
70 tion, we ñnd it advantageous to ñrst subject the
pulp to mechanical deaeration, by which substan
' tially all of the entrained air and from 85 to
90% of the oxygen dissolved in the solution, are
removed. 'I‘he remaining free oxygen can then
75 be completely removed or nulliñed by the intro
idly and effectively precipitated.
.
'I'hus following the mechanical deaeration op
eration in receiver I I, the pulp is shown being
subjected to agitation in the first compartment A
of -a closed series agitator I1. In compartment
A the pulp is intermixed with a.` suitable lead salt,
Since the
solution of the pulp is alkaline, the lead salt is 10
immediately converted to lead plumbite, which is
dispersed in the pulp, to be subsequently deposited
uniformly on the _finely divided zinc, where it
stimulates precipitation of the precious metals.
Chemical deoxidation of the pulp is indicated in 15
compartment B of agitator I1. To eiïect chemi
cal deoxidation for the removal of dissolved oxy
gen, We make use of an active chemical deoxidiz
ing agent, which is capable of existing in the
presence of alkalinity, such as a metal hydro
20
sulphite like zinc hydrosulphite, or an alkali hy
drosulphite like sodium or calcium hydrosulphite,
which is shown being introduced into compart
ment B of agitator I'I in controlled amounts.
Zinc dust precipitant, in the form of an emul 25
sion of zinc dust in water, is introduced into com
partment C, which in common with the other
compartments is closed to the atmosphere and
ñtted with a mechanical agitator. Precipitation
of the dissolved precious metals is effected in 30
compartment C and next succeeding compart
ment D. Instead of introducing the alkali hydro
sulphite and zinc emulsion separately, both may
be added simultaneously, as for example to com
partment B. Also, the alkali hydrosulphite may
be formed continuously as required by adding a
suitable amount of alkali bisulphite to the zinc
dust emulsiñer, the reaction between the` zinc
dust and the alkali bisulphite forming a hydro
sulphite. The reaction mixture, upon being in 40
troduced into the alkaline pulp, causes complete
elimination of free` oxygen and precipitation of
the metals. In typical instances the chemical
deoxidation and precipitation will b_e complete
in from 5 to 15 minutes. We have described the 45
deoxidation and precipitation as being conducted
in closed agitators, to eifect economy in reagents.
The operation may be practiced in open top agi
tators provided sufficient reducing agent is pres
ent and the surface of the pulp within the agi
50
tator fairly quiescent.
After the dissolved precious metals have been l
precipitated, the pulp is subjected to a stabilizing
operation for the purpose of inhibiting cyanogen
solvents for precious metals, which would other 55
Wise partially redissolve the -precipitated metals
in the subsequent flotation operation. This sta
bilizing or inhibition of the cyanogen solvents can
be satisfactorily carried out by addition of a suitL
able copper salt, like copper sulphate. Because 60
copper salts are more expensive than iron salts it
may be more economical in certain instances to
inhibit most of the cyanogensolvents with a suit
able iron salt, and then to complete the stabili
zatlon by the addition of a suitable copper salt 65
\ like copper sulphate. Thus the stabilizing opera
tion has been indicated in two stages in compart
ments E and Fî In the first, or preliminary sta
bilizing stage E, a suitable iron salt such as fer- .
rous sulphate or ferrous hydrate, is introduced 70
into the pulp in an amount slightly greater than
that theoretically required to combine with the
cyanogen compounds known to be present. The
ferrous sulphate immediately combines with the
cyanogen compounds which are chieñy free cy 75
3
2,111,600
‘anide and zinc cyanide, to form ferrous iron cy
anide compounds. In the second or final stage of
cally and eñiciently carried out in an alkaline cir
stabilizing F, a suitable copper salt such as copper `
cuit, that is, where the solution of the pulp is dis-`
tinctly alkaline to phenol phthalein. For each
sulphate is introduced into the pulp to complete
the inhibition of the cyanogen solvents present.
Following stabilizing, the pulp is-subjected to a
unit of silver precipitated by the zinc, a corre
sponding amount of alkali zinc cyanide is formed.
`Since the solution is alkaline, some of the zinc
flotation operation I8, for the recovery of a flota
. cyanide, in accordance with Well known reactions,
tion concentrate containing the desired precious
is immediately converted to free alkali cyanide
and alkali zincate,-. thus increasing the cyanide
strength and consequently the precipitation ac-_
tivity of the solution as deposition o_f `the silver
metal values.
‘
-
In many instances the precious metal values of
the flotation concentrate will consist mainly of
those precious metals which were dissolved by the continues.
'
cyanide solution and subsequently precipitated.l
Where the ore being treated contains oxidizing
In other instances where the precious metals or agents like manganese dioxide, there is no appre
15 precious metal minerals of the ore are not amen
.ciable increase in the consumption of hydrosul 15
able to ready extraction by the cyanide solution, phite or like deoxidizing chemical, because such`
the iiotation concentrate will consist in part of agents are relatively inert in an alkaline solution,
precipitated values, and in part of precious metals and will not react with the hydrosulphite. Since
or precious metal minerals which were not dis-V conditioning of the pulp for precipitation does not
20 solved by the cyanide solution.
involve -a neutralizing operation, the presence of
'I'he procedure described above, in which the ' calcium carbonates or likeacid consuming sub
zinc dust precipitant is ñrst reacted with alkali ' stances can cause no diiñculty, particularly if the
bisulphite, is a convenient procedure for the solution of the pulp remains alkaline throughout
the process.
I
,
»
formation of a hydrosulphite, and is also desir
able in that this preliminary reactiontends to
vThe term “ore” as used herein has reference in 25
brighten the zinc particles, thus rendering them general to gold and silver bearing deposits. Thus
more active precipitants. However, as'previously the process in certain -instances can be applied to
described, hydrosulphite can be supplied from tailings from previous metallurgical operations,
some other source, and introduced into >the pulp as well as to natural ore deposits which have not
30 while the pulp is beingragitated to effect chemical been previously treated. Also the process may be 30
‘deoxidatiorn after which zinc dust can be suitably combined with conventional cyanidation, as for introduced into the pulp as a separate operation. ‘
With respect to the introduction of a lead salt
' for coating the zinc particles with metallic lead,
35 it is obvious that the point at which this lead‘is
' \ introduced into the pulp may be modified to suit
lvarious requirements, and, if desired, the lead salt
and the zinc precipitant may be contacted and the
zinc particles thus coated with> metallic ¿lead before
40 the zinc is introduced into the pulp.
The stabilizing operation is a necessary feature
of the complete process, because if cyanogen sol
_vents for precious metals were not inhibited at thisl
point, a\ portion of the precipitated precious
45 metals, particularly gold,- would be redissolved in
the subsequent violent aeration of the notation
operation I8. However, when cyanogen solvents
are properly inhibited, the flotation operation can
be carried out by the use of standard flotation ap
50 paratus, with- known flotation reagents ~such as
xanthates, cresylic acid.` and pine oil, without ap
preciable re-solution of the precipitated metals.
Use of copper sulphate as described has been
found beneficial to flotation, particularly where
55 Xanthates are employed as ñotation reagents.
This is because metallic copper precipitates on the
zinc precipitant along withthe precious metals,
instance in the following manner. After crush
ing and grinding, the ore pulp may be classified
into sand and slime', that is,-into coarser and finer
portions. The sand then may be very economi a5,
cally leached with cyanide solution in open tanks
for high recoveries of gold and silver. The slime
may be treated by the process of the present in
vention. The equipment required is much simpler
and much cheaper than that heretofore used in
the conventional cyanidation of slime, and the
recoveries of silver and gold will in many cases,
be higher than heretofore obtained, owing to the
fact that the process recovers not only soluble
values but -also additional values occluded in 45
mineral particles.
e
In the cyanidation treatment of some ores, par
ticularly where the predominant precious metal isv
silver, the alkaline pulp, after dissolution of the
metals, may contain only relatively small amounts 50
of residual freeoxygen. In such cases, mechani
cal and/or chemical deoxidation of the pulp with
a chemical deoxidizing agentv such as alkali hy
vdrosulphite, may be dispensed with, the small
amount of free oxygen remain'ing'in the pulp 55
being nulliñed by the reducing action of the pre- >
cipitant itself, provided the amount of precipitant
and enters into reaction with xanthate to form employed/_is sufficient to precipitate thedesired
copper xanthate, which greatly facilitates flotation _ metal, in addition to serving asa reducing agent.
of the precious metal values.
_
u
y
.
Such a modified‘treatment is shown in outline
In order to secure proper precipitation of dis
drawing Fig. 2. The ore pulp, after dissolution
l solved precious metals, the process as disclosed
of the readily soluble precious metals in agitator
requires the presence of sufficient cyanide in the loa, is transferred by pump I2a to the first com
solution to properly activate the metallic pre
partment of the series mechanical agitator lla,
cipitant. Therefore, the process is particularly which is preferably closed to the atmosphere. To 65
adapted for use on ores of which the precious
metal values are predominantly silver, although
some gold may also be present. Relatively strong
cyanide solutions are required for the dissolution
7,0 of silver minerals and therefore in treating such
ores the solution will initially contain suiñcient
the pulp in compartment A, is added a precipi
tant such as zinc dust emulsion, together with
a soluble lead salt such as lead nitrate. vPrecipi
tation of the precious metals takes place in com
partments A, B and C, through which the pulp 70
free cyanide to properly dissolve both the gold and passes in series.
stabinzing of the pu1p, that 1s,-ini-libiuon of Vthe silver', and after dissolution the solution will
stillcontain suñicientlavßnide so that the pre ~ the cyanogen solvents for the precipitated 'pre
cipitation of the dissolved metals can be economi
cious metals can be carried out entirely by the 75
4
2,111,600
use of a copper salt, or in the manner previously
described with reference to Fig. 1, by the addition
of a soluble iron salt, such as ferrous sulphate,
to compartment D, and of a soluble copper salt,
such as copper sulphate, to compartment E, fol
lowing which the pulp ilows to a conventional
ñotation machine Illa. Flotation reagents are
added and the pulp subjected to flotation concen
tration, yielding a rougher flotation concentrate
10 and a tailing which is discharged to Waste.
The rougher concentrate may be subjected to
further cyanidation for the recovery of the con
tained precious metals, or it may be ñrst cleaned
or enriched in precious metals by refloating. For
15 this purpose the rougher concentrate may pass
to a second'flotation machine I9, with or without
the further addition of flotation reagents. The
enriched cleaner concentrate passes to further
treatment by conventional methods for ñnal re
20 covery of the precious metals, and the cleaner
tailings can be returned to cyanide agitator lila,
where they are subjected to further extraction by
cyanidation and then to re~precipitation and re
ñotation. Precious metal values contained in the
25 cleaner tailings or middlings, as they are called,
are frequently only slowly soluble in cyanide solu
tion, and the above described step of returning
the cleaner tailings to further cyanidation treat
ment, is a new and useful method of obtaining
30 higher recoveries of the precious metals from
many ores, and at the same time producing a
the recovery of precious metal values from ores,
forming a pulp consisting of comminuted ore
solids and alkaline cyanide solution ccfntaining
precious metals dissolved from the ore, precipi
tating dissolved precious metals in the pulp, intro
ducing iron salt into the precipitating pulp» to
combine with cyanogen solvents for. precious
metals, introducing a copper salt into the precipi
tated pulp to combine with residual cyanogen
solvents for precious metals, and then subjecting 10
the pulp to a ñotation operation for the recovery
of a flotation concentrate containing the desired
precious metal values.
»
4. In a cyanide process for the recovery of pre
cious metal values from ores, forming a pulp con
cyanide solution containing precious metals dis
solved from the ore, removing free oxygen from
'the pulp, precipitating dissolved precious metals
in the alkaline pulp, stabilizing the pulp by in 20
hiblting cyanogen solvents for the precious
metals, said stabilizingoperation including ñrst
introducing an iron salt into the pulp following
by introduction of a copper salt, and then sub
jecting the pulp to a flotation operation for the 25
recovery of the flotation concentrate containing
the desired precious metal values.
5. In a process of the character described for
the recovery of precious metal values from ores
containing oxidizing agents like manganese di 30
oxide, forming a pulp consisting of comminuted
high grade, cleaner concentrate for subsequent
ore solids and alkaline cyanide solution, and re
treatment or shipment to a smelter, which may
moving free oxygen from the pulp by introduc
tion of a hydrosulphite, while alkalinity of the
pulp is maintained to inhibit oxidation of the 35
hydrosulphite by the manganese dioxide of the
be desirable on some ores. The majority of the
35 copper or copper compounds resulting from the
introduction of copper sulphate, pass out with
the cleaner concentrate, and are therefore not
returned to the process. Return of substantial
amounts of copper to the agitator tank Illa would
40 be objectionable, because it,y would cause forma
tion of copper cyanides, thus requiring additional
cyanide to properly dissolve the precious metal
values and to activate precipitation.
This application is a continuation in part cfl
45 subject matter disclosed and claimed in our co
pending application Serial No. 41,768, ñled Sep
tomber 23, 1935.
We claim:
_ 1. In a process of the character described for
ore.
v
,
6. In a. process of the character described for
the recovery of precious metal values from ores
forming a pulp consisting of comminuted ore 40
solids and alkaline cyanide solution, containing
precious metals dissolved from the ore, precipi
tating the dissolved precious metals in the pulp,
adding a copper salt to the pulp, subjecting the
pulp to a flotation operation, and returning at 45
least a part of the flotation tailings for re
cyanidation and ilotation with solids of the ore.
7. In a process of the character described,
forming a pulp consisting of ñnely divided ore `
50 the recovery of precious metal values from ores,
solids, cyanide solution, and precipitated precious
forming a. pulp consisting of comminuted ore
metal values, subjecting the pulp to a flotation
solids and alkaline cyanide solution containing
precious metals dissolved from the ore, subjecting
the pulp to mechanical deaeratlon, subjecting the
55 mechanically deaerated pulp to chemical deoxida
tion, precipitating dissolved precious metals in
the pulp, stabilizing the pulp by inhibiting cyan
ogen solvents for the precious metals, and then
subjecting the pulp to a flotation operation for
operation by the use of xanthate as a flotation
60 the recovery of a notation concentrate containing
the desired precious metal values.
2. In a process of the character described for
the recovery of precious metals from ores, form
ing a pulp consisting of comminuted ore solids
65 and alkaline cyanide solution containing precious
metals dissolved from the o_res, 'subjecting the
pulp to mechanical deaeraticn, introducing an
alkali hydrosulphíte into the pulp whereby the
remaining free oxygen is removed, precipitating
70 dissolved precious metals in the pulp, stabilizing
the pulp by inhibiting cyanogen solvents for pre
cious metals, and then subjecting the pulp to a _
treatment for the removal of a concentrate con
taining the desired precious metal values.
75
15
sisting of comminuted ore solids and alkaline
3. In a process of the character described for
agent, and introducing copper sulphate into the
pulp prior to the flotation operation to prevent
resolution of precipitated precious metal values 55
and to aid in effecting eiiicient notation.
8. In a process of the characterdescribed for
the recovery of precious metal values from ores,
forming a pulp consisting of comminuted ore
solids and alkaline cyanide solution'containing 60
precious metals dissolved from the ore, precipi
tating the dissolved precious metal values in the
alkaline pulp, adding to the pulp a salt capable
vof combining with cyanogen solvents of precious
metals to form cyanogen compounds in which 65
precious metals are substantially insoluble, and
then subjecting the pulp to a flotation operation
for the recovery of a notation concentrate con
taining the desired precious'metal values, the
notation operation being characterized by aera 70
tion of the pulp.
9. In a process of the character described for
the recovery of precious metal values from ore,
forming a pulp consisting of comminuted ore
solids and alkaline cyanide solution containing
animo
precious metals dissolved from the ore, precipi
tion concentrate containing the desired precious
tating the dissolved precious metals in the alka
metal values.
line pulp, adding copper sulphate to the alkaline
14. In a processfor the recovery of precious
pulp in an amount in excess of that required to -metal values from a pulp consisting of com
‘combine With cyanogen solvents of precious minuted ore solids and cyanide solution contain
metal, thereby stabilizing the pulp, and then sub
ing dissolved precious metals, precipitating the
jecting the pulp to a flotation operation for- the dissolved precious metals in the pulp while the
recovery of a flotation concentrate containing the pulp contains a sulphite salt, stabilizing the pulp
desired precious metal values, said flotation op
by inhibiting cyanogen solvents for precious
10 eration being characterized by aeration of the metals, and then subjecting the pulp to a flota l0
pulp.
'
10. In a process of the character described for
the recovery of precious metal values from ores
containing oxidizing agents vlike manganese di
oxide, forming a pulp consisting of comminuted
ore solids and alkaline cyanide solution, and re
moving free oxygen from the pulp by the use of
a. sulphite salt, while alkalinity of the pulp is
maintained to inhibit oxidation of the sulphite
20 salt by tne manganese dioxide of the ore.
11. In a process for the recovery of precious
metal values from a pulp consisting of com
minuted'ore solids and cyanide solution contain
ing precious metals dissolved from the ore, ef
fecting precipitation of dissolved precious metals
in the pulp, stabilizing the pulp by destroying
cyanogen solvents for precious metals, and then
subjecting the pulp to a flotation operation for
the removal of a flotation concentrate containing
30 the desired precious metal values.
12. In a process for the recovery of precious
tion operation for the removal of a flotation con
centrate containing the desired precious metal
values.
,
15. In a process for the recovery of precious
metal values from a pulp consisting of com
minuted ore solids and cyanide solution contain
ing dissolved precious metalsjeffecting precipita
tion of the dissolved precious metals in the pulp,
stabilizing the pulp by reacting the same with
copper sulphate, and then subjecting the pulp to 20
a flotation operation for the removal of a flota
tion concentrate containing „the desired precious
metal values.
'
16. In a process for the recovery of precious
metal values from a pulp consisting of com 25
minuted ore solids and cyanide solution contain
ing precious metals dissolved from the ore, ef
fecting precipitation of the dissolved metals in
the pulp, by the use of zinc dust as a metallic
precipitant, introducing into the pulp metallic .
salt capable of combining with cyanogen sol- ,
metal values from pulp consisting of comminuted
vents for precious metals to form cyanogen com
ore solids and cyanide solution containing pre
cious metals dissolved from the ore, effecting pre
cipitation of dissolved precious metals in the pulp,
while the solution of the pulp contains a deoxi
pounds in which precipitated precious metals
are substantially insoluble, and then subjecting
the pulp to a flotation operation for the removal
of a flotation concentrate containing the desired
dizing agent, thereafter stabilizing the solution
precious metal values.
by destroying cyanogen solvents for the precipi
tated metals, and then subjecting the pulp to a
17. In a process for the recovery of precious
metal values from a pulp consisting of com
40 notation operation-for the removal of a flotation
concentrate containing the precious metal values
from the ore.
13. In a process for the recovery of precious
, metal values Afrom a pulp consisting of com
minuted ore solids and cyanide solution contain
ing precious metals dissolved from the ore, ef
fecting precipitation of dissolved metals in the
pulp, introducing into the pulp’a metallic salt
capable of combining with cyanogen solvents for
50 precious metals to form cyanogen compounds in
which precipitated precious metals are substan
tially insoluble, and then subjecting the pulp to
a flotation operation for the removal of a nota.
minuted ore solids and cyanide solution contain 40
ing precious metals dissolved from the ore, ef
fecting precipitation of dissolved metals in the
pulp, introducing into the pulp a chemical capa
ble of combining with cyanogen solvents for pre
cious metals to form cyanogen compounds in
which precipitated precious metals are substan
tially insoluble, and then subjecting the pulp to
a flotation operation for the removal of a flota
tion concentratecontaining the desired precious
values.
v
LOUIS D. MILLS.
THOMAS B. CROWE.
JDYE C. HAUN.
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