CA2131793C - Composition and method for agglomerating ore - Google Patents

Abstract

The binder composition for agglomerating ore fines of the invention is a mixture of (1) a reactive calcareous component, (2) a reactive siliceous and aluminous component, and (3) a sulfate compound.
Preferably, the binder composition is comprised of 10 to 80 % by weight lime as the calcareous component, 5 to 50 % by weight fly ash as the siliceous-aluminous component and to 80 % by weight sulfate compound such as gypsum. Most preferably, the siliceous-aluminous component is a low carbon content fly having less than about 0.5 % by weight carbon content. The preferred lime component of the binder composition is either a high calcium line with greater than about 90 % by weight CaO content ora dolomitic lime. In the process for recovery of metals from ores having ore fines of the metals, the ore fines are first agglomerated by adding thereto a binder composition, the binder composition comprising about 10 to 80 % by weight lime; 10 to 80 % by weight sulfate compound and 5 to 50 % by weight siliceous-aluminous material. A leach bed is formed of the agglomerated ore and the bed is leached with a leaching agent to there-by form a leach liquor. The metal values are recovered from the leach liquor.

Description

wo ~~m ~~ ~o ~ .~ ~ .~ ~ ~ ~ ~~ius~zmza 1 ~
~escrigtion C°om~osition and Method for Agglomerating, Ore Technical Field The present invention relates to the recovery of metal values from ores and, specifically to a process and composition for agglox~erating ore fines to enhance the economic recovery of metals in a heap leaching recovery pr~cess.
.. Bac~C~round Art The recovery of preci~us metal values by cyanide solutians, and leeching b~ virtue of the standard 1~ heap l~:ach process are l~cnowin in the a~~. S~g~h process are descra.bed,, f or examp:l a , in LT o S . Patent No .
3 , ?77 , 00~ , issued D~cem~aer 4 , 1.973 , to ~ankeraan et al.
It is well redogni~ed that the stag of Nevada ~o has extensive ore deposits of gold and silver. In these deposits, as well as in deposits in other states and localities, theme has been found to occur a~ appreciable amount. of fines, i.e., minus 40 mesh or finer, in the ore material. Such fires inhibit ~5 the degree of success that has previously been achieved in connection with recovery of precious metal values from such ores,. A great deal caf study has been conducted in connection with the character of such fines; resembling fine~parti~le clays o~
30 bentonitic type, and the effect of such fines in the presence of ores undergoing treatment for precious metal values.
In the prior art, heap leach piles and leaching solutions have been used with varying degrees of 35 success. Many such processes have not been ~la~~'1°I "~~'~ ~~-I~E°i' i%UO 93/18190 1P~"T/IJS92/02111 _ economically successful since tine finE plasterings over rocks and interstices of heap leach gales have prevented the advantageous recovery of pregnant solutions or have allowed leaching fluids to percolate therethrough. Tn order to economically heap leach gold and silver ores, it has thus been found necessary to agglomerate the ores before leaching can begin, using some type of binder. The agglomeration prevents migration of ore fines, swelling of clays, and collapse of the heap.
Migration of fines and swelling of clays can blind parts ,of the heap making efficient leaching impossible. Collapse of the heap can seal-up large areas ~o the leaching solution and channel the solution around areas where it is needed: ,fit the present time, high calcium lime and Portland cement are used as binders. Both of these binders have the advantage of maintaining the p1i of the leaching solution in the rangy from about 10-1~ which is necessary for leaching with a cyanide solution.
Lime, ~Ca(OI~)2, prevents the swelling of clay by replacing monovalent rations, Na+ and K+, with the divalent ration, Ca++. The presence of divalent rations prevents significant swelling of clays in the recovery process. Also, lime reacts with silica and alumina in the clays and ore fines giving calcium silicate and aluminates, hydrates binding the agglomerates together, thus preventing migration of fines and heap collapse.
In lPortland cement, calcium silicates and aluminates are already intimately mixed so that the hydrates form rapidly, giving good strength to the agglomerate. If the ore is of low clay content or the clay has a low pozzolinic activity, i.e., the low availability of silicates and aluminates, I have ~LJ~~TIT~.J°~'~ ~~°-~I~E'T°

VVO 9~/1~190 ~ ~ PCT/US92/0211'1 found that Portland cement will make a higher strength binder than lime. Portland cement has low free calcium hydroxide content, however, and accordingly is not as efficient as lime in preventing swelling of clays in high clay content ores.
The present invention has as its object the provision of an economical recovery technigue for precious metal values from metal ores through the use of an improved binder composition for agglomerating the ore fines. The technidue has particular applicability to the recovery of gold and silver.
Summary of the Invention The binder composition for agglomerating ore fines of the invention is a mia~ture of (1) a reactive calcareous c~mponent, (2) a reactive siliceous and aluminous Component, and (3) a sulfate comp~und.

Preferably, the binder composition is comprised of 1d7 to 80% by weight lime as the calcareous component, 5 zo to 50% by weight fly ash .as the siliceous~aluminous companent and 1~ to ~0% by weight sulfate compound such as gypsum. M~st preferably, the siliceous-aluminous component is a low carbon content fly ash having less than about o.5% by weight carbon content.

The preferred lime component of the binder composition is either a high calcium lime with greater than about 90% by weight Ca~ content or a dolomitic lime.

In the process for recovery of metals from ores having ore fines of the metals, the ore fines are first agglomerated by adding thereto a binder composition, the binder composition comprising about 10 to ~0% by weight lime, 10 to 80% by weight sulfate compound and 5 to 50% by weight silicious-aluminous material. A leach bed is formed of the agglomerated ~~..af3STl'~°~9'~'~ ~H'~E-I°

WO 9~/ I $19(1 PCT/US9Z/021 I 1 C r~

ore and the bed is leached with a leaching agent to thereby fox°ir:~ a leach lit~uor, The metal values are recovered from the leach liquor.
Additional objects, features, and advantages will be apparent in the written description which follows.
Detailed Description of the Invention The preferred binder composition of the 1~ invention comprises a mixture of (1) a reactive calcareous component such as lime (h~.gh calcium or dolomitic), (2) a reactive siliceous-alumi~ous, component, and (3) su~:fur or sulfate compound such as gypsum. The three component mixture of the invention produces a binder co~posi.tion for ore fine agglomeration with superior propert~:es to both lime and Portland cement.
The reactive calcareous component of the binder composition is an inorganic substance contaaning 2~ calcium mnd/or magnesium oxide or hydroxide or other form of chemically coaabined calca:um or magnesium which, under the conditions employed in the steps of the process, reacts with the siliceous, aluminous and sulfur components of the composition to form calcium, 25~ aluminous, sulfur, silica hydrates (e. g. ettringite and tobermorite) . The prefer>"ec~ reactive calcareous substance is high calcium quicl~ lime. the thigh calcium quick lime, Ca0 useful in the present invention has a Ca~ content of greater than about ~0~
30 by weight, preferably greater than about 95~ b~
weight. The reactive calcareous component is preferably present in the range from about 10 to 80~
by weight ~f the binder composition.
The binder composition also contains a reactive siliceous-aluminous component which is employed in aIJ~STITIJT~ ~'~-g~~T

W~~3/~~~9~ ~~ ~~ ~~~ PC'~'/CI~92/02111 _ making the calcium silicate, calcium aluminate hydrate product of the invention. "Such reactive silica~us-aluminous components include artificial or natural pozzolans, pulverized fuel ash (fly ash), granulated slag, pumice dust, ground silica, clays such aS bentonite or kaolinite, Portland Cement kiln dust and others, as well as anixtures thereof having a p~z~olanic character. Sy "pozzolan" is meant a finely divided material rich in silica or alumina which, while not necessarily cementitious in itself, will react at ordinary temperatures with hydrated ., lime in the presence of water to form cementitious.

product CJ s The preferred siliceous/aluminous component is a fly ash having a low carbon content. Fiy ash is a commercially available product whidh will be familiar to those skilled in the art. In the 192~s, a more effective method of firine~ power p~:ant boilers came into use consisting of the pulverizing ~f the coal into a fane powder, the addlt~.on oft a pra.mary azr, and the burning of the coal powder substantially in a suspended state within the furnace. Such coal. is pulverize, conveyed from the pulverizes with air into the furnace, and combustion ta~Ces place almost ix~~tantly while the fine coal particles are in a suspended state. This method of burning coal has come into wide use due to its increased efficien;~y of combustion. The ash content of the coal, which may ' vary from a low of about 4~ t~ a high of about 20~ or more, is subject to the intense heat of combustion which may run between 2,000 anc~ 2,800F. Most of the ash is in the form of fly ash: the discreet sphere-like par~icles which are converted upwardly with the flu gases and separated therefrom by electrostatic or mechanical collectors. A typical fly ash composition SUE~~TI°~'l.l'°9"E ~~~~"'~'°

VV~ 93/ i 8190 P(.'1'/LIS92/0211 I
r contains the following constituentse ~1120~, 15-35%:
Si02, 40-55%: Ee2~3, 5-25%: S03, 0-5%: FeSZ, 0-1%:
~igt~, 1-3%: CaO, 1-5%: TiC2, 1°°3%: C, 0°~5%.
The preferred fly ash component useful in the present invention has less than about 0.5% by weight carbon by direct carbon analysis. The fly ash component is present in the range from about 5 to 50%
by weight of the binder composition.
The preferred sulfate compound of the binder 20 composition is gypsum, a readily available mineral that needs only to be ground fob use in the binder _. composition. Preferably, the gypsum (CaS~4'2H20)is ground in the range from about 100%-10 mesh to about x.00%-200 mesh before making the binder composition.
Other sources of sulfates such as waste wall board or fossils fuel power plant liras scr'abber sludge can also be utilized.
The binder composit;.on ~.s itself used in the range from about 0.100 to 2.000% by weight of ore to be treated, preferably in the range from about 0.500 to 1.500% by weight of ore.
The mixture of high calcium lime, gypsum and low carbon content fly ash gives a binder composition for are fines ac~~lomeration with superior properties to both lime and Portland cement. Theoretically, this result can be explained as followse When hydrated, a reaction occurs between the lime, sulfate, anrl alumina in the fly ash to form ettringite, a calcium alumina sulfate hydrate. Microscopically, ettringite forms an interlocking set of rod-shaged crystals binding the ore fines together. The result is ore agglomerates with good strength properties even in low clay content ores. Calcium from both the lime component and the gypsum component of the binder composition can replace monovalent rations in ~1.~~'I°~~9TE ~h~E~"~' :..,,,: r..,..~..r:tr ....~.::'t , ,.".::~... .~;:~.. .:. ,,,,._: ."~:~.,~; , .".:':' ...,..~,:~, .r.~:;
~'1~'O h3/1~19Q ~ ~ ~ ~ r~ ~ ~ P'C~'/'~592/02111 swelling clays and prevent swelling. ~s a result, the binder composition of the invent.on is particularly well suited for use in high clay content ores.
.An ore is agglomerated by mixing the granulated ore with the dry binder composition. mater is then mixed with the binder composition-ore mixture to agglomerate the ore. The agglomerate can be air dried or cured in an oven. If a~.r cured in p~.ace, to t~ 2~ days, or preferably 7 to 10 days, is required to develop the desired strength. A Mach bed is then ., formed of the agglomerated ore f fines and the bed is leached with a leaching accent to form a leach liquor.
The metal values are recovereel from tae leach liquor in accordance with standard procedure.
The following example is intended t~ be '.11u '~Jtr~at~.~e of the Ln~ent,LOn s.
Exa~l~[.~la I
T~ test the strength of Ore agglomerates made with different binders, the -40 mesh fraction of an ore was separaaed out and port.~ns were mixed with ~%
by weight of the binders to be tested. Enough water was added to each mixture to form a thick waste and the pate placed in cube molds. The mixtures were Y
cured in the molds for twenty-four hours at x.20° F
~to simulate 30 days curing at room temperatures in to~~ relative humidity atmosphere. The cubs were then tested to failure to measure unconfined compressive strength. The binders tested and the strengths obtained are given in Table T.
~~.J1f3~1°'1'~'LJT~ ~h~~~'f' vv0 93/y8~9o ~cr/~~gz/oz~ ~ v _ _ s TAELE z Unconfined Compressive Strength After Curing Binder Composition 24 hours at 120° F
Type II Portland Cement 93. Lt p.s.i.
40% Hi°Cal QL, 22.5% Fly .Ash, 97.0 p.s.i.
37.5% Gypsum 40% Hi-Cal QL, 22.5% Clay, 95.0 p.s.i.
37.5% Gypsum ~5 40% Iii°~Gal QL, 22 . 5 % Fly Ash, 92 . 5 p. s ° i .
37 ° 5% Ground Gypsu~a 6~allboard 40% Dolomitic QL, 22.5% Fly Ash, 52.5 p.s.i.
37.5% Gypsum EF~LE 11 50 pounds of a minus ° inch fraction of a gold ore was treaded with 0.53 pounds of a birder c~mpositio~x made up of 4~% lime, 22.5% fly ash and 37,5% gypSUm, all percents being in parts by weight.
The gypsum had boen ground to pass a minus 30 mesh si~~e before making the binder composition.
Treatynent and agglomeration were carried: ~ut by placing the sir dry ore in the 55 gallon dsuxn of a drum roller. The dry binder composition was sprin7cled on top of the ore and the binder composition ° ore mixture was rotated in the drum at 1U RQhi fog 1 minute.
Appro~eimately ~., X20 milliliters of water was then slowly added while rotating the drum for 4 manut~s. The addition of the wetting agent caused the fans particles of ore to stick together o~ stick to the coarser particles to form an agglomerated ore.
Total weight of the aggiamerated are was 54.5 paunds.
~''u1.1E3~'TI'T'LJ'1'E .s.,''a~-'~~~T

'VV~ 93/1$190 ~ ~ ~ ~ ~ ~ ~ P~'/LJS92/02~ ~ l _ g Then, 51.5 pounds of the agglomerated ore mixture was placed in a lPlexiglass column of 5.25 inch internal diamEter, f~rx~ing a column of ~re 62 inches tall with a wet density of 66.3 pounds per cubic foot. Another 50 pound aliquot of the ore was agglomerated with 1,770 anilliliters of water in an identical manner without the binder composition.
51.5 pounds of this ore formed a column 57.75 inches tall, with a wet density of 71.2 pounds per cubic foot. The agglomerates curare allowed to cure for 7 days.
.. Both columns were leached at 200 milliliters per hour (0.006 gallons per minute per square foot) with a solution of water containing 0.05% sodium cyanide and 0.09% sodium ~nydrs~xide. The sodium hydroxide was added t~ bring the initial pH of the water into a range between~about 11 and 12. During the first 4 hours of leaching, the column containing the ogre heated with the binder composition of the invent:wn settled by 3.5 inches (2.4%) gi~ring an ore column k~eight of 60.5 inches and an ore density of 67.9 pounds per cubic foot> During the same 4 hours, the untreated ore settled by 7.75 inches (13.4%) to a coluxan height of 50 inches with an ore density of 82.2 pounds per cultic foot. After 4 hours of ~.eatsh~.ng, n0 further settlement Of th " Ore was detected.
A third c~lumn was also prepared in an identical manner using 0.50 pounds of Type 2 Portland cement and 1,760 milliliters of water for agglomeration.
The initial column height was 62.5 inches giving an ore density of 65.8 pounds per cubic foot. No settling of this column was detected during the leaching.
~~~T~T~'fi~ ~1°IE~T

WO l3/1$1~10 P~'>IJS92/02119 c~.~~~~~3 - -lo-It was noted that the leaching solution started to filter out the bottom of the Portland cement treated column in about 30 minutes while it took 4e5 hours for solution to begin filtering aut the bottom of the binder treated and untreated columns. This indicates ~ solution retention or holding capacity ~f about 100 milliliters in the Portland cement treated column and 800-1,000 milliliters in the other two columns.
7Leaching solution was c~llected and tested for pH, gold content, and cyanide content several tames during the leaching period. The values are given in Table II:
Table II
Leaching Solution Data From C~lumns Column ~. (N~ Treatment) 2o Leaching NaCN cumulative Gold Time (hrs.) ~ Concentratian Leached !mo) !~) ~.0 0.005 1.5:~

27 8.4 0.010 18.8 45 9.3 0.040 22.0 69 Stopped Leaching E~ecause of Low pH.

C~hamn 2 (Portland C~ment Tr~atment~
Leaching NaCN Cumulative: Gold Time Lhrs:Z pH Concentration !%) Leached lmr~

2 V 11 . 0 s 02 7 . 1 27 11.5 0.02 9.3 45 11.5 0.04 13.2 69 11.5 0.04 17.6 ~1.1~~TITtJT~ ~~~~T

WO 93/1190 '~ ~~ P~T/U~92/02111 C~~.umn 3 t~iaader Coa~~~s3.tz~xi) Leaching NaCN Cu~auZative Gold Time~hrs.) ~ Concentration (%) Leached tmc) 2 V ~ ~ 0 a 0 . ~

27 11. 0 a 03 ~.9 . 4 45 1.1. 0. 04 22 . 9 ~

69 1.~.. 0. 04 26. ~

Column ~4 t Lime Tr~at~d~nt Leaching NaCN Cumulative Gold .. Tine ~hrs.) ~ Concentration (%) heached (ma) 2 tD 11. 5 0 ~ 01 3 4 : 2 1.5 27 ~ ~~ a.J ~ s ~3 1.7 . ~.
~45 llaa 0a0~ 20~g ~~ ~~ s5 ~ s 0~ 23. 3 ~t can lbe seen from Table 1I that both the ~~rtland cement and bin~cier composition treatment keep the pN high enough t~ prevent excessa.ve cyanide losses. zt is believed that the low gold recoveries found for the Portland cement treatment are due to the low amounts of solution held on the ore, i.a~, ~5 the Portland cement does not allow the ore to t~et as well as the ore treated with the binder composition, si~wing down or preventing high gold recoveries.
~n invention. has been provided with several advantages. The improved binder composition of the invention produces an agglomerated ore with superior properties> In addition, the binder composition of the invention is more economical to manufacture than either Portland cement or lime alone.
While the invention has been shown in only one of its forms; it is not thus limited but is ~iJ~~l'I"~°L~°'~'°~ ~I~°~i~E"1' ~~,Y~y y~. , øt. . .. . t :. r .... :..as ..~.n.~.." .. . . ",. ..... , ... .. .., , , . ... ~ ~'~~ s. ~ .. .
'WO 93» ~19~ P'CTfUS92>02d l ~
- ~.2 -susceptible to various charges and z~~dificatiors without departing from the spirit thexeofa ~1J~3~P"I"i"I,~TE ~h-IEET

Claims (4)

Claims:

1. A heap leach bed which is leached with an aqueous cyanide leaching agent for recovering gold and silver metals, comprising:
granulated ore containing precious metal values selected from the group consisting of gold and silver metals;
a binder composition in an amount of 0.001 to 2.000%
by weight of ore mixed with the granulated ore, the binder composition comprising:
10 to 80% by weight lime 10 to 80% by weight gypsum;
5 to 50% by weight fly ash; and water added to the mixture of granulated ore and binder composition in an amount effective to form an agglomerated ore; and wherein said fly ash is low carbon fly ash having less than 0.5% by weight carbon.

2. The heap leach bed of claim 1, wherein the lime is a high calcium quicklime having greater than about 90% CaO content by weight.

3. The heap leach bed of claim 1, wherein said lime is a dolomitic lime.

4. The heap leach bed of claim 1, wherein said gypsum is calcium sulfate dehydrate.