Method for increasing metal production in smelter operations

The present disclosure pertains to methods for increasing production of metal values from sulfidic ores in smelting operations.

Smelting is a common method for recovering the desired metal value from sulfidic ores. During the smelting process, the sulfur in the ore is oxidized, resulting in an exothermic reaction, whereby the heat generated is sufficient to melt the metal without the need for an external heat source. Typically, a carbonaceous reducing agent, such as coke, is employed in the reaction.

Reverberatory smelters, sometimes called “copolas” are commonly used. The fuel and metal ore charge are usually fed separately. In the first step, two liquids are formed: one is an oxide slag containing the impurities, and the other is a sulfide “matte” containing the valuable metal sulfide and some impurities. Fuel is burned at one end of the furnace, and the heat melts the dry sulfide concentrate (usually after partial roasting) which is fed through the openings in the roof of the furnace. The slag floats on the top of the heavier “matte” and is removed or rejected. The sulfide matte then is forwarded to a converter.

Metal production during the smelting operation is limited by the upper temperature limitations of the smelting furnace. Due to the exothermic nature of the pyrometallurgical reduction, adding additional metal sulfide has the same effect as adding more fuel. In order to increase production, smelters can benefit from smelting ores with increased surface moisture since the moisture will evaporate, reducing the temperature of the upper furnace, and thereby allowing more ore to be fed to the furnace, resulting in an increase in metal production.

While adding moisture to a sulfidic ore prior to smelting provides benefit, the amount of moisture added is limited due to problems that may be associated with increasing ore moisture content, such as caking and clogging of conveyor belts and other conventional ore transport means.

The present invention involves improvement of metal value yield in smelting processes of the type in which a sulfide containing metal ore is smelted. An aqueous solution or dispersion comprising a surfactant is brought into contact with the ore. In this manner, higher moisture content ores can enter the smelter, allowing for an increase in the amount of ore processed per given time period, and therefore an increase in metal production.

In accordance with one exemplary embodiment, an aqueous solution or dispersion comprising a surfactant is applied to the sulfidic ore prior to entry into the smelter. Preferably, the surfactant may be applied in the form of an aqueous foam.

With respect to foam formation, air is preferred for use as the foam forming gas. Details of the foam forming process are not critical to the invention. Generally, foam may be produced as stated in U.S. Pat. No. 4,700,200 (Cole), the disclosure of which is incorporated herein. Typically, the aqueous based surfactant is mixed with air at a ratio of about one gallon liquid with from about 1-100, preferably 1-10, scf air. The air and liquid may combine at a point immediately upstream from the mixing chamber. The mixing chamber may be a packed column, venturi, or static mixer. The purpose of the mixing chamber is to induce the air in liquid dispersion that is defined as a “foam”. Acceptable foam properties include expansion ratios (volume foam:volume liquid) on the order of about 10-100. Average bubble size is on the order of about 200 microns or less. Exemplary feed rates would range from about 0.1-1.0 pounds of active surfactant per ton of metal sulfide.

Exemplary surfactants that can be used include the anionic surfactants and non-ionic surfactants. Preferably, the non-ionic surfactants have an HLB of between about 10-15. Blends of the aforementioned surfactants can also be mentioned.

Suitable anionic surfactants include sulfates and sulfonates such as alkyl aryl sulfonic acids, alkyl sulfonic acids, alkenyl sulfonic acids, sulfonated alkyls, sulfonated alkyl ethers, sulfonated alkenyls, sulfated fatty esters, and the sulfosuccinates.

The term anionic surfactants should be broadly construed to include the anionic detergents such as the long chain alpha olefin sulfonates, water soluble salts of alkenyl sulfonic acid, such as the sodium salt of C 14 -C 18 alpha olefin sulfonates, water soluble alkyl aryl sulfonic acid salts, such as sodium alkylnaphthalene sulfonate and sodium alkyl benzene sulfonate and water soluble salts of lauryl sulfate.

Particularly preferred anionic surfactants are esters represented by the formula

wherein R is an aliphatic carbon chain containing at least one sulfonic group and R 1 and R 2 may be the same or different, but are chosen from alkyl groups having from 3 to about 18 carbon atoms. Most preferred are the succinic acid esters such as the dioctylester of sodium sulphosuccinic acid.

Exemplary non-ionic surfactants include alkyl phenols, such as the polyalkylene alkyl phenols; polyalkoxylated alkyl phenols; polyoxyalkylene polymers and block copolymers, glycol esters, glycol ethers including diethylene glycol esters, and diethylene glycol ethers, and polyalkylene glycols.

Specific non-ionic surfactants that may be mentioned include polyethylene nonyl phenol, polyethoxylated nonyl phenol, polyoxyethylene polymers and polyoxypropylene polymers, (EO) ethylene oxide (PO) propylene oxide polymers, polyethylene oxide octyl phenol ether, polyoxyethylene glycol dioleate, propylene glycol, and diethylene glycol ethers such as the “carbitol” series and diglymes.

Exemplary compounds falling within the classification of diethylene glycol ether compounds include diethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monoethyl ether, diethylene glycol dibutyl ether, diethylene glycol monohexyl ether, diethylene glycol monomethyl ether, and diethylene glycol monomethyl ether acetate. Additionally, diglyme (diethylene glycol dimethyl ether), ethyl diglyme (diethylene glycol diethyl ether), and tetraglyme (tetraethylene glycol dimethyl ether may also be mentioned.

Accordingly, the diethylene glycol ether compounds may be defined as having the formula:

R 3 —(O-Et-O-Et-O) n —R 4   (II)

wherein R 3 and R 4 are independently selected from the group consisting of C 1 -C 8 lower alkyl, acyl and hydrogen; n is equal to 1 or 2. Of these, diethyleneglycol monobutyl ether (sometimes referred to as butyl carbitol) is preferred.

Preferably, the foam or other carrier containing the surfactant or surfactant blend is fed to the sulfidic ore in an amount of about 0.01 to about 5.0 pounds of active surfactant(s) per ton of metal sulfide. More preferably, from about 0.01 to 1.0 pounds of surfactant(s) is fed per ton of metal sulfide.

Any sulfidic ore that is to be smelted may benefit from the invention. For example, the surfactant treatment may be applied to sulfidic ores such as Au, Fe, Ag, Ni, Cu, Zn, Pb, and Mo ores.

Field Trial

At one zinc smelting operation, ZnS ore was treated with a foamed surfactant formulation comprising on all actives bases

45 wt % sodium dioctyl sulfosuccinate 9.65 wt % propylene glycol 25.70 wt % diethylene glycol monobutyl ether remainder water.

Typically, the ZnS ore fed to the smelter had a moisture content of about 10% as received. Normally, when the ore was sprayed with water to increase the moisture content to about 12.0 wt %, flow and plugging problems were encountered. When the above surfactant blend was foamed onto the ore, moisture contents of from 12.0 to about 14.0 wt % could be processed without significant hopper blockage, transport or plugging problems.

While this invention has been described with respect to particular embodiments thereof, it is apparent that numerous other forms and modifications of this invention will be obvious to those skilled in the art. The appended claims and this invention generally should be construed to cover all such obvious forms and modifications which are within the true spirit and scope of the present invention.