METHODS OF USING THE SAME

Technical Field of the Invention This invention relates to aqueous metal dithiophosphates and methods of using the same useful in ore processing. In this invention, the metal dithiophosphate is present in an amount greater than 65% by weight.

Background of the Invention

Dialkyldithiophosphoric acids and salts thereof such as the sodium, potassium or ammonium salts have been utilized as promoters or collectors in the benefication of mineral-bearing ores by flotation for many years. Often, these metal dithiophosphates are aqueous metal dithiophosphates. However, concentrated versions of metal dithiophosphates, those generally containing higher levels of sodium dithiophosphate may be gelatinous. These gelatinous materials are difficult to handle. For transportation and handling purposes, it is desirable to have concentrated liquid aqueous metal dithiophosphates. Shipping costs are greatly reduced as the amount of aqueous diluent is decreased in the metal dithiophosphates.

Early references to dithiophosphate salts and their use as flotation promoters may be found in, for example, U.S. Patents 1,593,232 and 2,038,400. The dialkyldithiophosphoric acids utilized as flotation promoters and collectors for sulfide and precious metal ores are obtained by reacting an alcohol with phos¬ phorus and sulfur generally as P ₂ S ₅ . The acid obtained in this manner can then be neutralized to form a salt.

U.S. Patent 3,086,653 describes aqueous solutions of alkali and alkaline earth metal salts of phospho-organic compounds useful as promoters or collectors in froth flotation of sulfide ores. The phospho-organic compounds are neutralized P ₂ S ₅ -alkanol reaction products. Although single alcohols are normally used in the reaction, the patentees disclose that mixtures of isomers of the same alcohol, and mixtures of different alcohols may be utilized as starting materials in the preparation of the phosphorus compound, and the resulting acidic products can be readily neutralized to form stable solutions which are useful as flotation agents.

U.S. Patent 3,570,772 describes the use of di(4,5-carbon branched primary alkyl) dithiophosphate promoters for the flotation of copper middlings. The 4 and 5 carbon alcohols used as starting materials may be either single alcohols or mixtures of alcohols. U.S. Patent 4,879,022 issued to Clark et al relates to a dithiophosphorus acid or salt used in a flotation process utilizing sulfurous acid. Thionocarbamate is disclosed as an auxiliary collector.

Procedures for the selective flotation of copper minerals from copper sulfide ores wherein a slurry of ore and water is prepared and sulfurous acid is added to the slurry to condition the slurry prior to the froth flotation step have been discussed in, for example, U.S. Patents 4,283,017 and 4,460,459. Generally, the pulp is condi¬ tioned with sulfur dioxide as sulfurous acid under intense aeration, and then subjected to froth flotation.

Summary of the Invention This invention relates to a liquid composition, comprising: greater than about

65% by weight of an alkali or alkaline earth metal salt of a thiophosphorus acid having hydrocarbyl groups each independently containing from about 2 to about 8 carbon atoms; and at least about 1% by weight water.

In another aspect, the invention relates to an oil-free liquid composition, comprising: greater than about 65% by weight of an alkali metal salt of a thiophosphorus acid having hydrocarbyl groups each independently containing from 2 to about 8 carbon atoms, and water.

The liquid compositions of this invention have low water content. These compositions are easy to handle and have reduced transportation costs. These materials are liquid at room temperature and are especially useful as ore flotation agents.

Detailed Description of the Invention The term "hydrocarbyl" includes hydrocarbon, as well as substantially hydrocarbon, groups. Substantially hydrocarbon describes groups which contain non-hydrocarbon substituents which do not alter the predominantly hydrocarbon

nature of the group.

Examples of hydrocarbyl groups include the following:

(1) hydrocarbon substituents, that is, aliphatic (e.g., alkyl or alkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, aromatic-substituted aliphatic substituents or aromatic-substituted alicyclic substituents, or aliphatic- and alicyclic- substituted aromatic substituents and the like as well as cyclic substituents wherein th ring is completed through another portion of the molecule (that is, for example, an two indicated substituents may together form an alicyclic radical);

(2) substituted hydrocarbon substituents, that is, those substituent containing non-hydrocarbon groups which, in the context of this invention, do no alter the predominantly hydrocarbon nature of the substituent; those skilled in the ar will be aware of such groups (e.g., halo (especially chloro and fluoro), hydroxy, alkoxy, mercapto, alkylthio, nitro, nitroso, sulfoxy, etc.);

(3) hetero substituents, that is, substituents which will, while having predominantly hydrocarbon character within the context of this invention, contain a atom other than carbon present in a ring or chain otherwise composed of carbo atoms. Suitable heteroatoms will be apparent to those of ordinary skill in the art an include, for example, sulfur, oxygen, nitrogen and such substituents as, e.g., pyridyl furyl, thienyl, imidazolyl, etc. In general, no more than about 2, preferably no mor than one, non-hydrocarbon substituent will be present for every ten carbon atoms i the hydrocarbyl group. Typically, there will be no such non-hydrocarbon substituent in the hydrocarbyl group. In one embodiment, the hydrocarbyl group is purel hydrocarbon.

In the specification and claims, liquid compositions refer to composition which are liquid at room temperature, i.e., about 20°C.

Liquid Compositions

The liquid compositions of the present invention are alkali or alkaline eart metal salts of thiophosphorus acids. These compositions generally contain water an greater than about 65%, or greater than about 70%, or greater than about 75%, o even greater than about 80% by weight of the metal salt. The metal salt may b

present in an amount up to about 90%, or about 95% by weight of the liquid composition. Typically, the alkali or alkaline earth metal salt of a thiophosphorus acid is present in an amount from about 80% to about 90% by weight of the liquid composition. Thiophosphorus Acids

The thiophosphorus acid contains one or more hydrocarbyl groups having from about 2, or about 3, or about 4 to about 8, or to about 6, or to about 5 carbon atoms. In one embodiment, the hydrocarbyl groups are alkyl or cycloalkyl groups, preferably alkyl groups. The hydrocarbyl groups of the thiophosphorus acid are each independently ethyl, propyl, butyl, pentyl, hexyl or octyl groups. The hydrocarbyl groups of the thiophosphorus acids are each independently derived from many of the monohydroxy organic compounds listed below.

In one embodiment, the phosphorus acid contains one linear hydrocarbyl group and one branched hydrocarbyl group. Examples of linear hydrocarbyl groups include primary propyl, butyl, pentyl, hexyl and octyl groups. Examples of branched hydrocarbyl groups include isopropyl, isobutyl, secondary butyl, 4-methyl-2-butanol, methylamyl, and 2-ethylhexyl groups.

The thiophosphorus acids include thiophosphoric; thiophosphinic; or thiophos¬ phonic acids. Use of the terms thiophosphoric, thiophosphonic and thiophosphinic acids is meant to encompass monothio as well as dithio forms of these acids. The thiophosphorus acids are known compounds and may be prepared by known methods. Preferably, the thiophosphorus acid is a dithiophosphoric acid.

In one embodiment, the thiophosphorus acid may be represented by the Formula X

(RJrP-XH (I)

wherein each Rj is independently a hydrocarbyl, hydrocarbyloxy, or a hydrocarbylthio group having from 2 to about 8 carbon atoms and each X i independently oxygen or sulfur, provided that either one R. is a hydrocarbylthio

group or one X is sulfur. Preferably, each R, is independently an alkyl, aryl, alkoxy aryl, aryloxy, alkylthio or arylthio group, more preferably an alkyl, aryl, alkoxy o aryloxy group, with an alkoxy or aryloxy group being more preferred.

Preferably, each Rj independently contains from 2, or about 3, or about 4 t about 8, or to about 6 carbon atoms. In one embodiment, each Rj independentl contains 4 or 5 carbon atoms. Examples of Rj include propyl, propoxy, propylthio butyl, butoxy, butylthio, amyl, amyloxy, amylthio, methylamyl, methylamylox methylamylthio, hexyl, hexyloxy and hexylthio groups. The above list is meant t include all isomeric arrangements of the above groups. For instance, butyl is mea to include isobutyl, sec-butyl, n-butyl, etc.

In another embodiment, one Rj is linear and one Ri is branched. Example of branched R _t groups include isopropyloxy, isopropyl, isopropylthio, isobutyloxy isobutyl, isobutylt io, sec-butyloxy, sec-butyl, sec-butylthio, sec-amyloxy, sec-amy sec-amylthio, methylamyloxy, methylamyl, and methylamylthio groups. Example of linear or Rj groups include linear versions of the list of Ri groups above. In on embodiment, one Ri is a isobutoxy group and the other Rj is an amyloxy or methylamyloxy group. In one embodiment, each R _x may be independently derive from any of the hydroxy organic compounds listed below.

In Formula I, X may be oxygen or sulfur, more preferably sulfur. In on embodiment, one X is oxygen and the other X is sulfur. In another embodimen each X is sulfur.

Thiophosphorus acids are known to those in the art. Preferably th thiophosphorus acid is a dithiophosphoric acid. Dithiophosphoric acids are know compounds and may be prepared by the reaction of a hydroxy-containing organi compound such as an alcohol and a phenol or a mixture of hydroxy-containin organic compounds with a phosphorus sulfide such as phosphorus pentasulfide. Th dithiophosphoric acids generally are prepared by reacting from about 3 to 5 mole more generally 4 moles of the hydroxy-containing organic compound (alcohol phenol) with one mole of phosphorus pentasulfide in an inert atmosphere temperatures from about 50 °C to about 200 °C with the evolution of hydrogen sulfid

The reaction normally is completed in about 1 to about 3 hours.

The hydroxy organic compounds are generally monohydroxy organic compounds. These compounds include alcohols and their substituted derivatives, e.g., nitro-, halo-, alkoxy-, hydroxy-, carboxy-, etc. Suitable alcohols include, for example, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-propanol,

1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-l-butanol, 3-methyl-2-pentanol, 1-hex- anol, 2-hexanol, 3-hexanol, 4-methyl-2-pentanol, 2-methyl-3-pentanol, cyclohexanol, 2-chlorocyclohexanol, heptanol, 2-ethylhexanol, 1-octanol, 2-octanol, etc. The aliphatic alcohols containing from about 4 to about 6 carbon atoms are particularly useful in preparing the dithiophosphoric acids.

In one embodiment, the composition of the thiophosphorus acid is obtained by the reaction of a mixture of hydroxy-containing organic compounds with a phosphorus sulfide. The thiophosphorus acid is actually a mixture of thiophosphorus acids wherein one hydrocarbyl group may be derived from the same hydroxy compound as the other hydrocarbyl group, or one hydrocarbyl group may be derived from a different hydroxy compound than the other hydrocarbyl group. For example, when a thiophosphorus acid is prepared from a mixture of isobutyl alcohol and n-amyl alcohol, the thiophosphorus acid is actually a mixture of diisobutyl thiophosphorus acid, di-n-amyl thiophosphorus acids, and isobutyl, n-amyl thiophosphorus acids. Typical mixtures of alcohols and phenols which can be used in the preparation of thiophosphorus acids and salts include: isobutyl alcohol and n-amyl alcohol; sec-butyl alcohol and n-amyl alcohol; isopropyl alcohol and n-hexyl alcohol; isobutyl alcohol and n-amyl alcohol.

Salts of Thiophosphorus Acids Salts of the above thiophosphorus acids may be prepared by techniques known to those in the art. The acids are usually reacted with metal bases.

The metal bases are alkali or alkaline earth metal compounds. The alkali or alkaline earth metal compounds are typically oxides or hydroxides of alkali or alkaline earth metals. These compounds include sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium oxide, potassium oxide, calcium hydroxide and magnesium

hydroxide.

The metal of the metal salt is an alkali or alkaline earth metal, or just an alkali metal. Alkali metals include sodium, potassium, or lithium. In one embodiment, th metal of the metal salt is an alkaline earth metal, such as calcium or magnesium. Mixtures of alkali and alkaline earth metals may also be used such as calcium an sodium mixtures as well as mixtures of calcium with potassium.

As described above, the liquid compositions of the present invention contai water. In one embodiment, the liquid compositions contain at least about 1 %, o about 2%, or about 5%, or even about 8% by weight of the liquid composition. I another embodiment, the liquid compositions contains up to about 35%, or to abou

25%, or to about 20%, or to about 15% by weight water.

In another embodiment, the liquid composition contains generally less tha about 0.5%, or less than about 0.1 %, or less than about 0.05% by weight of an oil In one embodiment, the liquid composition is oil-free. It is understood that the ter "oil-free" means substantially oil free. In another embodiment, the salt of th thiophosphorus acid contains generally less than about 0.5 % , or less than about 0.1% or less than about 0.05% by weight of an oil. In another embodiment, the salt of th thiophosphorus acid is oil-free, i.e., contains no oil.

Preparation of the Salts In one embodiment, the liquid compositions are prepared by reacting thiophosphorus acid with an aqueous solution or dispersion of one or more of th above-described alkali or alkaline earth metal compounds. The aqueous solution or dispersions generally contain from about 25%, or about 35% to about 75%, or t about 65% by weight water. One useful aqueous solution or dispersion is a 50% b weight aqueous solution or dispersion of sodium hydroxide.

The aqueous solution or dispersion of the metal compounds is then mixed a a temperature from about 0°C, or about 15 °C, or about 20 °C to about 40° C, or t about 60°C, or even to about 100°C. The reaction is generally exothermic. Th water content of the liquid composition is established by the water content of th alkali or alkaline earth metal solution or dispersion. For instance, when

dithiophosphoric acid is neutralized with a 50% aqueous solution of sodium hydroxide, the water resulting from the neutralization of the acid as well as the water from the alkali or alkaline earth metal solution or dispersion would then be the water content of the liquid composition. Lower water contents could be obtained by evaporating or removing water, such as by vacuum stripping, as is known to those in the art.

Li another embodiment, the thiophosphorus acid may be neutralized using a solid alkali or alkaline earth metal compound and a little water or alcohol, i.e., enough water or alcohol to provide enough contact for the neutralization of the thiophosphorus acid. In still another embodiment, the thiophosphorus acid may be treated with a combination of a solid alkali or alkaline earth metal compound and a solution or dispersion of the alkali or alkaline earth metal compound.

The inventor has discovered that dithiophosphoric acids having the particular hydrocarbyl groups having from about 2 to about 8 carbon atoms form aqueous metal salts which are liquid under ambient conditions. Ambient temperatures generally are those from about 20°C to about 30°C. The low water content of some. of the liquid compositions of the present invention provides beneficial low temperature properties, such as decreased pour point, to the liquid compositions. Also, these materials are easy to handle and have reduced transportation costs. i another embodiment, the liquid composition of the present invention may contain an alcohol. The alcohol may be any alcohol which does not adversely affect the liquid composition. An example of these alcohols are any alcohols listed individually or in the mixtures above. A particularly useful mixture of alcohols includes the mixture of isobutyl alcohol with either methylamyl or amyl alcohols. These alcohols are useful in any proportion, however, a particularly useful proportion includes from about 45 to about 75, preferably about 65 mole percent of isobutyl alcohol and from about 25 to about 55, preferably about 35 mole percent of amyl alcohol or methylamyl alcohol. The alcohol may be added prior to formation of the metal salt or after the formation of the metal salt. The alcohol may also be present in the thiophosphorus acid and is the alcohol used to make the thiophosphorus acid.

The alcohols may be present in an amount from about 0.05%, about 2%, or abo 5%, or about 10% up to about 33%, or to about 25%, or to about 15% by weight the liquid composition. In one embodiment the alcohol is present in an amount fro about 5%, or about 7% up to about 15%, or to about 12% by weight of the liqui composition.

Metal salts of phosphorodithioic acids may be referred to as "mixed metal" "multiple metal" salts or complexes. The salts may be prepared as described abov Alternatively, the mixed metal salts may be prepared by reacting a metal salt of phosphorodithioic acid with an additional metal-containing reactant. This reactio may additionally be performed in the presence of a catalytic amount of an alkali alkaline earth metal oxide, hydroxide, halide or carbonate. The catalyst metal wi not be the same as the metal of the metal-containing reactant. In general, a catalyti amount contains about 0.001 to 0.05 equivalents of an alkali or alkaline earth met per equivalent of phosphorus in the acid or its salt. The mixed metal phosphorodithioic acid salts and methods for making t same are disclosed in U.S. Patents 4,466,895 and 4,089,793 and PCT Publishe International Application WO 89/06237, the disclosures of which are hereb incorporated by reference for their teachings related to mixed met phosphorodithioates and processes for making the same. The liquid compositions of the present invention are described in the followin examples. Unless otherwise indicated in the following examples, and elsewhere the specification and claims, all parts and percentages are by weight and a temperatures are in degrees Celsius.

Example 1 A reaction vessel is charged with 291 parts (3.64 equivalents) of a 50 aqueous solution of sodium hydroxide. An isobutyl, primary amyl dithiophospho acid, prepared by reacting phosphorus pentasulfide with 65 mole percent of isobut alcohol and 35 mole percent of primary amyl alcohol, is added to the reaction vess dropwise over 3 hours. The reaction temperature is maintained between 35 °C an 40°C. After adding the dithiophosphoric acid, the reaction mixture is stirred for o

hour. The reaction mixture if filtered through diatomaceous earth and the filtrate is the desired liquid dithiophosphate. The product has 7.74% phosphorus, 17.65% sulfur, 6.11% sodium, 15.8% water, and 9.3% of the alcohol mixture used to make the isobutyl primary amyldithiophosphoric acid. Example 2

A reaction vessel is charged with 254 grams (3.175 equivalents) of a 50% aqueous solution of sodium hydroxide. An isopropyl, methylamyldithiophosphoric acid, prepared by reacting phosphorus pentasulfide with 60 mole percent of isopropyl alcohol and 40 mole percent of methylamyl alcohol, is added to the reaction vessel dropwise over 0.5 hours. The reaction temperature is maintained below 45 °C. After adding the dithiophosphoric acid, the reaction mixture is stirred for one hour. The reaction mixture is filtered through diatomaceous earth and the filtrate is the desired liquid sodium dithiophosphate. The product has 10.1% phosphorous, 8.3% sodium, 18.2% sulfur, 16.8% water and 9% of the alcohol mixture used to make the isopropyl methylamyldithiophosphoric acid.

Example 3 A reaction vessel is charged with 661 grams (8.26 equivalents) of a 50% aqueous solution of sodium hydroxide. An isopropyl, methylamyldithiophosphoric acid is added to the reaction vessel dropwise over 1.5 hours. The reaction temperature is maintained between 45°C and 47°C. After adding the dithiophosphoric acid, the reaction mixture is stirred for 0.5 hours. The product has 6.9% phosphorous, 16.5% sulfur, 6.3% sodium, 15.5% water and 9.4% of an alcohol mixture of 60 mole percent of isopropyl alcohol and 40 mole percent of methylamyl alcohol. Example 4

A reaction vessel is charged with 91 grams (1.38 equivalents) of a 50% aqueous solution of sodium hydroxide. An isopropyl, octyldithiophosphoric acid is added to the reaction vessel dropwise over 0.5 hours. The reaction temperature is maintained below 45°C. Twenty grams of water is added to the vessel. The reaction mixture is filtered through diatomaceous earth and the filtrate is the desired liquid

sodium dithiophosphate. The product has 6.5% phosphorous, 15.2% sulfur, 5.6 sulfur, 19.7% water and 8.8% of an alcohol mixture of 60 mole percent of isoprop alcohol and 40 mole percent of isooctyl alcohol.

Example 5 A reaction vessel is charged with 160 grams (2 equivalents) of a 50% aqueo solution of sodium hydroxide, 200 grams of an alcohol mixture comprising 65 mo percent of isobutyl alcohol and 35 mole percent of methylamyl alcohol, and 40 gra of distilled water. A methylamyldithiophosphoric acid is added to the reaction vess dropwise over 1.25 hours. The reaction temperature is maintained below 60° After adding the dithiophosphoric acid, the reaction mixture is stirred for 1 hou

The product has 12.0% sulfur, 14.6% water and 7.5% methylamyl alcohol.

Example 6 A reaction vessel is charged with 174 grams (2.17 equivalents) of 50 aqueous solution of sodium hydroxide. An n-butyl,isopropyldithiophosphoric acid prepared by reacting phosphorous pentasulfide with 50 mole percent n-butyl alcoh and 50 mole percent of isopropyl alcohol, is added to the reaction vessel dropwi over three hours. The reaction temperature is maintained between 40 °C and 50° After adding the dithiophosphoric acid, the reaction mixture is stirred for two hour The reaction mixture is filtered through diatomaceous earth and the filtrate is t desired liquid sodium dithiophosphate. The product has 19.8% sulfur, 17.5% wat and 4.2% of an alcohol mixture of 50 mole percent of isopropyl alcohol and 50 mo percent of n-butyl alcohol.

Example 7 A reaction vessel is charged with 298 grams (3.72 equivalents) of 50 aqueous solution of sodium hydroxide. An isobutyl,amyldithiophosphoric acid added to the reaction vessel dropwise over three hours. The reaction temperature maintained between 40 °C and 45 °C. After adding the dithiophosphoric acid, t reaction mixture is stirred for one hour. The reaction mixture is filtered throu diatomaceous earth and the filtrate is the desired liquid sodium dithiophosphate. T product has 17.64% sulfur, 15.4% water and 9.2 % of the alcohol mixture of Exam

1.

Example 8 A liquid potassium dithiophosphate is prepared by the procedure described in Example 1 except 408 parts (3.64 equivalents) of a 50% aqueous solution of potassium hydroxide is used instead of the sodium hydroxide solution.

Example 9 A product is prepared by the procedure described in Example 1 except the alcohols of the dithiophosphoric acid are removed by vacuum stripping the dithiophosphoric acid to 70°C and 15 mm Hg for one hour prior to addition to the reaction vessel.

Example 10 A product is prepared by the procedure of described Example 9 except the dithiophosphoric acid of Example 3 is used instead of the dithiophosphoric acid of Example 1. Ore Flotation Processes

The liquid compositions of this invention are useful in processes for beneficiating an ore. In particular, the process is useful for beneficiating ores and recovering ^' metal values such as gold, copper, lead, molybdenum, zinc, etc. In one embodiment, the process comprises (A) forming a slurry comprising at least one mmeral-containing ore, water and a collector which is at least one liquid composition of the present invention; (B) subjecting the slurry from step (A) to froth flotation and recovering a mineral from the froth. In another embodiment, the slurry (step A) is formed with a water base composition containing the liquid compositions of the present invention diluted such as with water. The froth flotation process is useful to beneficiate mineral and metal values including, for example, gold, copper, lead, molybdenum, zinc, etc. Gold can be beneficiated as native gold or from such gold-bearing minerals as sylvanite (AuAgTe^ and calaverite (AuTe). Silver can be beneficiated from argentite (Ag ₂ S). Lead can be beneficiated from minerals such as galena (PbS) and zinc can be beneficiated from minerals such as sphalerite (ZnS). Cobalt-nickel sulfide ores such as siegenite or

linnalite can be beneficiated in accordance with this invention. Copper can b beneficiated from such ores as chalcopyrites (CuFeSj), calcocite (Cu ₂ S), covellit (CuS), bornite (Cu ₅ FeS ₄ ) and copper-containing minerals commonly associate therewith. In the following description, however, comments primarily will be directe toward the benefication and recovery of gold minerals, and it is intended that suc discussion shall also apply to the other above-identified minerals.

The ores which are treated in accordance with the liquid composition of th present invention must be reduced in particle size to provide ore particles of flotatio size. As is apparent to those skilled in the art, the particle size to which an ore mus be reduced in order to liberate mineral values from associated gangue and non-valu metals will vary from ore to ore and depends upon several factors, such as, fo example, the geometry of the mineral deposits within the ore, e.g., striations agglomerations, etc. Generally, suitable particle sizes are minus 10 mesh (100 microns) (Tyler) with 50% or more of the particles passing 200 mesh (70 microns)

The size reduction of the ores may be performed in accordance with any metho known to those skilled in the art. For example, the ore can be crushed to abo minus 10 mesh (1000 microns) size followed by wet grinding in a steel ball mill t specified mesh size ranges. Alternatively, pebble milling may be used. The proced ure used in reducing the particle size of the ore is not critical to the method of thi invention so long as particles of effective flotation size are provided.

Water is added to the grinding mill to facilitate the size reduction and t provide an aqueous pulp or slurry. The amount of water contained in the grindin mill may be varied depending on the desired solid content of the pulp or slurr obtained from the grinding mill. Conditioning agents may be added to the grindin mill prior to or during the grinding of crude ore. Optionally, water-soluble inorgani bases and/or collectors also may be included in the grinding mill.

At least one collector is added to the grinding mill to form the aqueous slurr or pulp. The collector may be added prior to, during, or after grinding of the crud ore. The above liquid compositions are useful as collectors.

The amount of the collector included in the slurry to be used in the flotation process is an amount which is effective in promoting the froth flotation process and providing improved separation of the desired mineral values. The amount of collector included in the slurry will depend upon a number of factors including the nature and type of ore, size of ore particles, etc. In general, the amount of collector is from about 0.5 to about 500 parts of collector per million parts of ore, preferably about 1 to about 50, more preferably about 1.5 to about 40.

In the process, a base may be used to provide desirable pH values. Desirable pH values are about 8 and above, preferably about 8 to about 13, more preferably about 9 to about 12, with about 10 to about 12 being highly preferred. Alkali and alkaline earth metal oxides and hydroxides are useful inorganic bases. Lime is a particularly useful base. In the process of the present invention, it has been discovered that the addition of a base to the ore or slurry results in a significant increase in the gold assay of the cleaner concentrates. The slurries will contain from about 20% to about 50% by weight of solids, and more generally from about 30% to 40% solids. Such slurries can be prepared by mixing all the above ingredients. Alternatively, the collector and inorganic base can be premixed with the ore either as the ore is being ground or after the ore has been ground to the desired particle size. Thus, in one embodiment, the ground pulp is prepared by grinding the ore in the presence of an inorganic base. The collector is added to the ground pulp and this mixture is thereafter diluted with water to form the slurry. The amount of inorganic base included in the ground ore and/or the slurry prepared from the ore is an amount which is sufficient to provide the desired pH to the slurry. Generally, the amount of inorganic base is from about 250 to about 2000 parts of inorganic base per million parts of ore, preferably from about 375 to about

1500.- This amount may be varied by one skilled in the art depending on particular preferences.

In step (B), the slurry is subjected to a froth flotation and a mineral is recovered from the froth. Most of the gold values are recovered in the froth (concen- trate) while significant quantities of undesirable minerals and gangue remain in the

underflow. The flotation stage of the flotation system comprises at least one flotatio stage wherein a rougher concentrate is recovered, and/or one or more cleaning stage wherein the rougher concentrate is cleaned and upgraded. Tailing products from eac of the stages can be routed to other stages for additional mineral recovery. The gold rougher flotation stage will contain at least one frother, and th amount of frother added will be dependent upon the desired froth characteristi which can be selected with ease by one skilled in the art. A typical range of froth addition is from about 20 to about 50 parts of frother per million parts of ore.

A wide variety of frothing agents have been used successfully in the flotatio of minerals from ores and any of the known frothing agents may be used in th process of the present invention. By way of illustration, such frothing agents straight or branched chain low molecular weight hydrocarbon alcohols such as C alkanols, 2-ethylhexanol and 4-methyl-2-pentanol (also known methylisobutylcarbinol, or MIBC) may be employed as well as pine oils, cresyl acid, polyglycol or monoethers of polyglycols and alcohol ethoxylates.

In one embodiment,, the collector is included in the slurry in step (A), an additional collector may be added during the flotation steps including the rough stage as well as the cleaner stage. In addition to the liquid compositions of t present invention, other types of collectors normally used in the flotation of ores m be used. These auxiliary collectors also may be added either to the rougher stage the cleaning stage, or both.

The froth flotation step may be improved by the inclusion of auxilia collectors in addition to the collectors of the present invention. The most comm auxiliary collectors are hydrocarbon compounds which contain anionic or cation polar groups. Examples of auxiliary collectors include fatty acids, fatty acid soap xanthates, xanthate esters, xanthogen formates, thionocarbamates, dithiocarbamate fatty sulfates, fatty sulfonates, mercaptans, and thioureas.

In the flotation step (B), the slurry is frothed for a period of time whi maximizes mineral recovery. The precise length of time is determined by the natu and particle size of the ore as well as other factors, and the time necessary for ea

individual ore can be readily determined by one skilled in the art. Typically, th froth flotation step is conducted for a period of from 2 to about 20 minutes and mor generally from a period of about 5 to about 15 minutes. As the flotation ste proceeds, small amounts of collectors may be added periodically to improve th flotation of the desired mineral values. Additional amounts of the collector of th present invention may be added periodically to the rougher concentrate and include in the slurry.

When the froth flotation has been conducted for the desired period of time, gol-eferpugher concentrate is collected, and the gold rougher tailing product is remove andrf ay be subjected to further purification.

The recovered gold rougher concentrate is processed further to improve th gold-grade and reduce the impurities within the concentrate. One or more cleane flotation stages can be employed to improve the gold grade to a satisfactory leve without unduly reducing the overall gold recovery of the system. Generally, tw cleaner flotation stages have been found to provide satisfactory results.

Prior to cleaning, however, the gold rougher concentrate is finely regroun to reduce the particle size to a desirable level. In one embodiment, the particle siz is reduced so that 60% of the particles are less than 400 mesh (35 microns). Th entire gold rougher concentrate can be comminuted to the required particle size or th rougher concentrate can be classified and only the oversized materials comminute to the required particle size. The gold rougher concentrate can be classified b well-known means such as hydrocyclones. The particles larger than desired ar reground to the proper size and are recombined with the remaining fraction.

The reground gold rougher concentrate then is cleaned in a conventional wa by forming an aqueous slurry of the reground gold rougher concentrate in water

One or more frothers and one or more collectors are added to the aqueous slurry o the reground gold rougher concentrate. This slurry is then subjected to a frot flotation. The collector utilized in this cleaner stage may be one or more of th collectors of the present invention and/or any of the auxiliary collectors describe above. In some applications, the addition of a collector and a frother to the cleanin

stage may not be necessary if sufficient quantities of the reagents have been carri along with the concentrate from the preceding gold rougher flotation. The durati of the first gold cleaner flotation is a period of from about 5 to about 20 minutes, a more generally for about 8 to about 15 minutes. At the end of the cleaning stage, t froth containing the gold cleaner concentrate is recovered and the underflow whi contains the gold cleaner tailings is removed. In one preferred embodiment, the g cleaner concentrate recovered in this manner is subjected to a second cleaning sta and which the requirements for collector and frother, as well as the length of ti during which the flotation is carried out to obtain a satisfactory gold content a recovery can be readily determined by one skilled in the art.

In one embodiment, the slurry in step (A) is subjected to conditioning. T conditioning acts to suppress iron. The conditioning step is especially useful w copper ores. After the ore slurry has been prepared in accordance with any of t embodiments described above, it is useful in some flotation procedures to conditi the slurry by adding cyanide, ammonium sulfide, sodium sulfide, lime or sulfuro to the slurry. Conditioning with sulfur dioxide occurs under aeration at a pH of fr about 5.5 to about 7.5. The conditioning medium may be an aqueous solution form by dissolving sulfur dioxide in water forming sulfurous acid (H ₂ SO ₃ ). In general, t amount of sulfur dioxide utilized in the conditioning step is within the range of fr about 500 to about 5000 of sulfur dioxide per million parts of ground ore. The of the conditioned slurry should be maintained between about 5.5 and about 7.5, m preferably between about 6.0 to about 7.0. A pH of about 6.5 to about 7.0 particularly preferred for the conditioned slurry.

Conditioning of the slurry is achieved by agitating the pulp contained i conditioning tank such as by vigorous aeration and optionally, with a suitable agita such as a motor-driven impeller, to provide good contact between the finely divi ore and the above conditioning agents. The pulp is conditioned sufficiently long maximize depression of the undesirable minerals and gangue while maximizi activation of the desired minerals such as copper minerals. Thus, conditioning ti will vary from ore to ore, but it has been found for the ores tested that condition

times of between about 1 to 10 minutes and more generally from about 3 to 7 minutes provide adequate depression of the undesirable minerals and gangue.

When using the sulfurous acid conditioning step, the flotation of copper is effected in the copper rougher stage at a slightly acidic pulp pH which is generally between about 6.0 and 7.0, the pH being governed by the quantity of sulfur dioxide used during the conditioning and aeration as well as the quantity of any inorganic base included in the slurry.

While the invention has been explained in relation to its preferred embodiments, it is to be understood that various modifications thereof will become apparent to those skilled in the art upon reading the specification. Therefore, it is to be understood that the invention disclosed herein is intended to cover such modifications as fall within the scope of the appended claims.