Background of the Invention Xanthates are organic compounds which are used in a variety of commercial processes, including, for example, the manufacture of rayon and for mineral collectors in froth flotation.

Flotation processes are used for recovering and concentrating minerals from ores. In froth flotation processes, the ore is crushed and wet ground to obtain a pulp. Additives such as mineral flotation or collecting agents, frothers, suppressants, stabilizers, etc., are added to the pulp to assist in separating valuable materials from undesirable or gangue portions of the ore in subsequent flotation steps. The pulp is then aerated to produce a froth at the surface. The minerals which adhere to the bubbles or froth are skimmed or otherwise removed, and the mineral-bearing froth is collected and further processed to obtain the desired minerals.

Xanthates are the salts of xanthic acids which are substituted dithiocarbonic acids of the type ROCSSH, in which R is ordinarily an alkyl radical. Unless otherwise designated, xanthic acid is generally understood to be the ethyl derivative. Thus, xanthates have the general formula shown below where R is an alkyl group. The alkyl group is typically between 2 to about 8 carbons long. M is an alkali metal such as Na or K.

RO-CS2-M The simpler xanthate salts, sodium as well as potassium ethyl, propyl, or butyl xanthates, are used as flotation collectors.

Xanthates are conventionally made by bubbling CS2 through a slurry of an appropriate alcohol to give the desired alkyl group. The slurry also includes ground sodium or potassium hydroxide in a volatile organic solvent such as pentane. The reactions involved are shown below.

ROH + NaOH ~ RONa + H2O RONa + CS,-ROCS2Na The xanthate produced from this process generally contains some water from the alcoholate (RONa) formation. Xanthate slowly reacts with water to form the alcohol and CS2.

So the formed xanthate almost immediately begins to decompose.

Another problem with the conventional production route for xanthates is that excess sodium or potassium hydroxide is needed with alcohols to form the alcoholate because alcohols are only weak acids. Excess hydroxide and water tend to promote the side product of sodium trithiocarbamate (Na, CS3). This product is a depressant for many sulfide minerals. The role of depressants, such as sodium trithiocarbamate, is discussed in, for example, U. S. Patent Nos.

4,510,050 and 4,584,118.

Brief Summary of the Invention The subject invention provides materials and methods useful for the efficient production of xanthates. Advantageously, the methods of the subject invention facilitate the cost-effective production of high purity xanthates.

The xanthate production process of the subject invention has three major steps. When all three steps are performed, it is possible to efficiently produce high purity xanthates having the following formula: RO-CS2-M wherein R is an alkyl group and M is an alkali metal. In a preferred embodiment, the alkyl group has from 2 to about 8 carbon atoms, and M is sodium or potassium.

The subject invention further pertains to the practice of each individual step in the 3-step xanthate production process. Through the practice of the individual steps, it is possible to, for example, produce alkali metals at a low cost. In a further embodiment, high value aluminum chloride is produced efficiently.

In a preferred embodiment, the process of the subject invention comprises an initial step whereby an alkali metal is produced inexpensively. Thus, one embodiment of the subject invention provides a unique and efficient source of alkali metals. A further product of this first step can be aluminum chloride.

Although the alkali metals produced in the first step of the xanthate production process can be used for a variety of purposes, in a preferred embodiment, the metal is used in subsequent method steps of the subject invention to produce excellent yields of high purity xanthates.

In the second step of the xanthate production process, metal produced in the first step is used to produce anhydrous alcoholate. High purity xanthate can then be produced by reacting the anhydrous alcoholate with carbon disulfide.

Detailed Disclosure of the Invention The subject invention provides a unique and advantageous method for producing xanthates. The method of the subject invention is particularly advantageous because it can be used to produce high purity xanthates at a low cost. The method of the subject invention is additionally advantageous because individual steps of the procedure can be used to produce useful products. Thus, these individual steps of the xanthate production process are, themselves, important embodiments of the subject invention.

In one embodiment, the subject invention pertains to a process for the production of low cost alkali metals. In accordance with the subject invention, this metal can then be used in the second step of the xanthate production process to produce an anhydrous alcoholate. This anhydrous alcoholate can then be reacted with carbon disulfide to form high purity xanthate.

Alternatively, the alkali metal product in step one can be used for purposes other than production of xanthates.

The xanthate production process of the subject invention has three major steps. When all three steps are performed, it is possible to efficiently produce high purity xanthates having the following formula: RO-CS2-M wherein R is an alkyl group and M is an alkali metal. In a preferred embodiment, the alkyl group has from 2 to about 8 carbon atoms, and M is sodium or potassium.

Using the process of the subject invention, xanthates of almost any variety can be produced. In one example, sodium tertiary butyl xanthate can be produced with a greater than 90% yield and a purity of greater than 95%.

Although the xanthate process of the subject invention has three major steps, any single step can be performed as a stand-alone reaction. The first reaction is used primarily to produce low cost alkali metals. Powdered aluminum is mixed and briquetted with an alkali metal salt such as sodium chloride. In a preferred embodiment, the mixture is briquetted using standard techniques. The mixture is then heated until the exothermic reaction occurs. An aluminum salt such as aluminum chloride then sublimes from the reaction zone, and the molten alkali metal drains from the reaction zone. Thus, both reaction products are removed from the reaction zone, driving the reaction to completion. As the stoichiometry indicates, one mole of aluminum will yield three moles of the alkali metal.

The reaction equation is shown below along with the pertinent thermochemical information: 3NaCI + Al-AICI3 + 3Na

Melting and Boiling Points for Species Involved in Na Metal Production Chemical Melting Point, °C Boiling Point, °C Al 660 2500 AlCl-Sublimes : 180 Na 98 882 NaCl 801 1465 Since the aluminum chloride sublimes as a high purity anhydrous product, controlled deposition of the sublimate facilitates selection of specific particle size distributions. This process provides an efficient means for producing a high value aluminum chloride for use in a variety of products including, but not limited to, deodorants and drying aids. If excess aluminum chloride is produced, such material can be utilized in making inorganic flocculants such as polyaluminum chloride. Hence, the low cost production of xanthate without the variability of the chloroalkali markets is possible.

Once an alkali metal has been produced, it can be reacted with an alcohol or an alcohol mixture that is the precursor of the desired xanthate. The alkali metal reacts with the alcohol rapidly, provided the reaction mixtures are anhydrous. Hydrogen gas is liberated which can then be flared or used as a reductant. For example, if hydrochloric acid is a desired product, the liberated hydrogen can be reacted with aluminum chloride to give HCI gas and aluminum. The reaction of the product of the alkali metal and the alcohol will be an alkali metal alcoholate as shown in the reaction equation below.

R-OH + Na-R-ONa + 1/2 H, The resultant alcoholate dissolved in an anhydrous organic carrier can be reacted with carbon disulfide to give the desired xanthate. This reaction is shown below.

R-ONa + CS2-ROCS2Na The process of the subject invention is particularly advantageous because no caustic agent is used to make the xanthate; therefore, no trithiocarbonate depressants result from the reactions. The use of sodium trithiocarbonate as a depressant for copper minerals in the differential flotation of molybdenite is known. Currently available commercially produced

xanthates contain sizeable amounts of trithiocarbonate depressants; thus, the ultra high purity anhydrous xanthates produced by the processes of the subject invention can be utilized at lower dosages. These xanthates are readily wetted by, or dissolved in, other non-aqueous collectors and frothers.

The greatest hindrance to the dissolution of suspension of xanthates that are currently available is the water contained in these xanthates. The xanthates produced by the methods of the current invention make excellent starting materials for collectors such as xanthogen formates, dixanthogens, thionocarbamates, and thioureas. Because the decomposition of xanthates is accelerated by the water creating hydrolysis, the anhydrous xanthate prepared by the process described herein has an excellent shelf life. The shelf life can be optimized by storage under nitrogen in air-tight containers.

It should be understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application.