BACKGROUND OF THE INVENTION: Air pollution from airborne dust is a problem in many mining operations such as copper mining. Since open pit copper mines are usually located in desert areas, haul roads and points of ore transfer such as dump pockets and conveyer belt transfer points are particular sources of dust.

Conventional mine dust suppression methods typically comprise spraying a solution of a dust suppressant composition onto surfaces that normally generate dust such as haul roads, etc. These compositions and methods are summarized in U. S. patent 5,223,165, the entire contents of which are incorporated herein by reference.

The methods and compositions described in U. S. 5,223,165 are not all satisfactory for use in open pit copper mining operations using solvent extraction for metal recovery because many of those surfactants used in the spray solutions interfere with the phase separation step. More specifically, in open pit copper mining operations wherein the ore is referred to as oxide ore, the copper is recovered from the ore by leaching with aqueous acid. The leaching is accomplished by trickling aqueous acid, such as dilute sulfuric acid, over and through pieces of ore having a relatively large surface area.

The leach solution dissolves salts of copper and other metals as it trickles through the ore, to provide an aqueous solution of the mixture of metal values. The aqueous solution is mixed in tanks with an extraction reagent which is dissolved in an organic solvent, e. g., a kerosene. This is commonly referred to as the organic phase. The reagent includes an extractant

chemical which selectively forms metal-extractant complex with the copper ions in preference to ions of other metals. The step of forming the complex is called the extraction or loading stage of the solvent extraction process. The organic phase is transferred to a large settling tank, where the organic solvent, now containing the copper-extractant complex in solution, is separated from the depleted aqueous solution (aqueous phase). This part of the process is called phase separation. Usually, the process of extraction is repeated through two or more mixer/settler stages, in order to more completely extract the desired metal. The process is described in detail in U. S. patent 4,582,689, the entire contents of which are incorporated herein by reference.

If the ore that is used is coated with some surfactants, the phase separation does not occur cleanly. That is, the surfactant acts as an emulsifier, causing the organic and aqueous phases to become suspended in each other thereby retarding the rate of phase separation and creating a ragged interface as opposed to a sharp, well-defined interface. The ill-defined interface is characterized by the presence of elongated drops of organic material suspended from the organic phase into the lower aqueous phase.

This undesirable material is generally referred to as"rag"and either fails to separate or separates only after a long period of time thus adding cost to the entire process.

It would be desirable to use a dust suppressing composition in open pit copper mining operations which causes minimal interference with the phase separation step of the extraction process for the recovery of heavy

metals from their ores such as the recovery of copper from copper ore in open pit mining operations.

BRIEF SUMMARY OF THE INVENTION: The surprising discovery has been made that dust suppressing compositions containing alkyl polyglycosides that exhibit low wetting times and weak emulsifying properties cause minimal interference with the phase separation step of the extraction process for the recovery of heavy metals from their ores such as the recovery of copper from copper ore in open pit mining operations. Such alkyl polyglycosides have alkyl groups that contain an average of from 8 to 12 carbon atoms and a degree of polymerization of from 1.4 to 1.6. Such alkyl polyglycosides rapidly wet the solid material such as rocks and dust etc., onto which they are applied, retard the rate of water evaporation from the applied solids, exhibit acceptable foaming levels and are environmentally acceptable in that they are readily biodegradable and exhibit low toxicity and favorable aquatic and eco-toxicity. The present invention relates to a process for suppressing dust which comprises contacting a particulate solid in a substantially dry environment with an effective amount of an aqueous solution of an alkyl polyglucoside or alkyl polyglucoside mixture of the formula I R1o (Z) a I wherein Ri is a monovalent alkyl radical having on average from 8 to 12 carbon atoms; Z is a glucose residue; a is a number having a value from 1.4 to 1.6.

The above alkyl polyglucosides and mixtures thereof also provide

rapid phase disengagement, clean interface after phase separation, rapid kinetics of copper extraction, good selectivity for copper over iron extraction, low tendency for foaming (important when diluting and filling water trucks), and low viscosity for ease of handling.

DETAILED DESCRIPTION: The process according to the invention relates to the suppression of dust from a particulate, friable solid. By"dust"is meant any particulate solid material that is susceptible to suspension in air or other atmospheric environment. Accordingly, the term dust includes particles having an average diameter of up to 1 cm (though typically only up to about 300 micron) and down into the fume range (e. g. typically as low as 0.001 micrometers). The particulate friable solid will be in a substantially dry, non-fluid environment, e. g. the solid will be comprised of less than about 15% by weight water. The friable solids can have a varying chemical composition. Examples include stones, ores particles, organic materials e. g. sawdust, grain dust, fiber dust, or animal waste, and mineral particles, especial silicic or carbonaceous minerals, e. g. coal dust, soil dust (humus and/or subsoil), gravel dust, fine clay, lime dust, fly ash, and the like.

The alkyl polyglucosides or mixtures thereof that are useful in the process according to the invention are those of the formula I RlO (Z) a I wherein Pi is a monovalent organic radical having an average of from 8 to 12 carbon atoms; Z is a glucose residue; a is a number having a value from 1.4 to 1.6. Such alkyl polyglucosides are commercially available, for example,

as APGO, GLUCOPONs, PLANTAREN@ or AGRIMULO surfactants from Cognis Corporation, Ambler, PA., 19002. Examples of such surfactants include but are not limited to: 1. GLUCOPON 220 Surfactant-an alkyl polyglucoside in which the alkyl group contains 8 to 10 carbon atoms, an average alkyl group size of about 9.1 carbon atoms, and having an average degree of polymerization of 1.5.

2. APG 325 Surfactant-an alkyl polyglucoside in which the alkyl group contains 9 to 11 carbon atoms and having an average degree of polymerization of 1.6.

3. GLUCOPON 425 Surfactant-an alkyl polyglucoside in which the alkyl group contains 8 to 16 carbon atoms, an average alkyl group size of about 10.3 carbon atoms, and having an average degree of polymerization of 1.45.

The GLUCOPON 425N surfactant is identical to GLUCOPONe 425 except that it has been neutralized.

Related Cognis surfactants that are however, outside the scope of the invention, include the following: 1. GLUCOPONe 225 Surfactant-an alkyl polyglucoside in which the alkyl group contains 8 to 10 carbon atoms, an average aikyt group size of about 9.1 carbon atoms, and having an average degree of polymerization of 1.7.

2. GLUCOPONo 625 Surfactant-an alkyl polyglucoside in which the alkyl group contains 12 to 16 carbon atoms, an average alkyl group size of about 12.8 carbon atoms, and having an average degree of polymerization of 1.6.

Solutions of the alkyl polyglucosides are applied to solid materials capable of forming dust particles as described above. These aqueous solutions can be placed in contact with the friable solid material in any manner effective to suppress the generation of dust therefrom. For example, the composition can be sprayed on a friable solid prior to or even during activity i. e. the imposition of mechanical stress (e. g. compaction, shearing, grinding, grading, shoveling, and the like) which causes the generation of dust from the solid. The aqueous composition can also be atomized (i. e. misted) into a atmosphere comprised of a finely divided solid to both aid in precipitation or settling of the solid and in minimizing regeneration of dust from the precipitate.

The amount of the alkyl polyglucoside in the spray solution is an effective amount which is any amount effective to suppress the generation of dust from the friable solid onto which the solution is applied. Typically, the amount will be from about 10 ppm to about 1000 ppm of alkyl polyglucoside in water with the preferred amount being from about 25 ppm to about 100 ppm.

In addition to the above alkyl polyglucosides, these aqueous solutions can also contain a hydrophilic binder material, such as an acrylic latex or a polysaccharide.

The invention will be illustrated but not limited by the following examples.

EXAMPLES Example 1 The following dust suppressants were tested by a standard QC extraction performance test that was conducted using 5v/v% 5-nonyl-2- hydroxyacetophenone oxime with Cu/Fe aqueous feed spiked with surfactant at the indicated level of active component. The results are set forth in Table 1 below: TABLE 1 50 ppm active, surfactant Undiluted Surfactant Ave. C's in Degree of Phase Sep, Interface Foaming Rate Viscosity, In alkyl Polym'n sec cps GLUCOPON 9.1 1. 5 96 clean 225 ml max 2800 220 GLUCOPONO 10.3 1.6 95 Clean 850 ml max 550 425 GLUCOPON 12.8 1.4 48 Some rag ND 21,500 625a DUSTCON @a NR NR 200 Heavy rag 1200 ml in 3.5 min ND

(a) not according to the invention NR = not relevant ND = not determined Discussion GLUCOPON 625 is not according to the invention because it's average alkyl group size is 12.8 carbons. DUSTCON is not according to the invention because it is does not contain an alkyl polyglucoside.

GLUCOPONe 625 is undesirable for two reasons. (1) It contributes to the formation of"rag"at the organic/aqueous interface after phase separation.

This is believed due to the higher average carbon length of the alkyl chain, causing a greater tendency to stabilize emulsions. Rag is a relatively stable network of organic film that is suspended from the interface in the aqueous phase. Solvent extraction is normally conducted in continuous mixer-settlers, so that mulsion from the mixer must continuously and rapidly coalesce in the setter. If organic matter, such as "rag", builds up excessively, it will be swept out of the settler with the aqueous phase and be lost from the solvent extraction unit. If the rate of phase separation is too slow (see DUSTCONs), the mulsion itself will be swept out of the settler; this is known as"flooding:, and constitutes an emergency situation that is dealt with by shutdown of the solvent extraction unit or by much slower flow rates. (2) The viscosity of undiluted

material is very high. It would need to be diluted several times with water to be practical to handle in a mining situation. Typically, the surfactant is diluted as the mining water trucks are filled with water. This takes place in a very short time, and the turbulence when filling the truck provides the agitation to mix and dilute the surfactant from a high concentration (25%- 50%) to the application concentration (typically 25-50 ppm, or 0.0025 to 0.0050%). A very high viscosity material would not only be difficult to pump, it would be slow to disperse to a uniform concentration.

DUSTCONo is also undesirable for three reasons. (1) Its heavy rag level will promote substantial entrainment of organic phase. (2) The slow phase disengagement rate will tend to cause flooding, limiting the rate at which liquids can be passed through a mixer-settler. (3) The higher tendency for foaming means greater problems when water trucks are filled.

Example 2: 1. PERFORMANCE DATA a. Batch SX Data The standard QC extraction performance test was conducted using 5 v/v% 5-nonyl-2-hydroxyacetophenone oxime with Cu/Fe aqueous feed spiked with surfactant at the indicated level of active component. The following abbreviations are used in all the tables below.

1-DUSTCON is a commercial dust suppressant which is a trademark product of Nalco, Inc.

2-E60 is the copper extraction point at 60 seconds.

3-E300 is the copper extraction point at 300 seconds.

4-Fe300 is the amount of iron extracted at 300 seconds.

5-Cu/Fe is the copper/iron ratio.

6-Kinetics refers to the amount of copper extracted at 60 seconds as a % of the amount at 300 seconds.

7-Phase Separation is the time required for the mulsion to separate completely into distinct organic and aqueous phases.

Series 1 Surfactant None DUSTCON' ppmActive Blank 50 ppm E60, g/3.92,3. 90 3.91, 3.99 E300,g/l3 4. 4.06 Fe3004, mg/ 1.2,1.1 3. 9,3.9 36271048,1041Cu/Fe53433, Kineticss 94,98% 96,98% Phase Sep, 65,75 s 233, 177 s sec. clean heavy rag Series 2 Surfactant Blank GLUCOPON# GLUCOPON# 1 : 1 625 220 GLUCOPON 625: 220 ppm Active none 50 ppm 50 m 25: 25 ppm E60, g/l 3.84,3.93 3.27,3.27 3.79,3.81 3.56,3.55 E300, g/l 3.99,3.99 3.91,3.96 11 4.06,3.99 Fe300, mg/l 48 38 63 1.95, 2.01 Cu/Fe 2696,1616,1664 2509,2521 2082,1985 2696 Kinetics 96,98% 84,83% 93,93% 88,89% Phase Sep 106,109s 47,48 s 97,94 s 81, 76 s sec. clean rag clean sl. rag Series 3 Surfactant Blank DUSTCONs GLUCOPON 220 GLUCOPON GLUCOPON# 425 425 ppm none 200 ppm 200 ppm 200 ppm 50 ppm Active E60, g/l 52 3.51,3.53 E300, g/l 4. 3.70 3.47,3.58 4.09,4.02 3.90 mu/ ! * Cu/Fe 1864,1913 590,611 798,827 785, 622 1099,905 Kinetics 95,96% 99,99% 71,76% 71,70% 86,88 Phase 108,105 clean 124,122?, 106 105,109s?, 95 Sep sec. heavy rag rag some rag clean

c. Foaming Data Dynamic foam cell evaluations were conducted in which the foam level in a 2L graduated cylinder is measured while circulating the solution and injecting onto the top at 4Umin. The following data was obtained using 115 ppm hardness water, which corresponds to the water from a commercial mining operation used for road spraying. Times given are those required to reach 1200 ml foam volume, or descriptive results if 1200 ml wasn't reached.

50 ppm Active: DUSTCONe: 3.5 min.

GLUCOPONs 425N: Reached 850 ml in 3 min, then decreased to 600 ml.

GLUCOPON@220UP: Remained between 200-250 ml foam.

75 ppm Active: DUSTCON2': 2.5 min.

GLUCOPON#425N : 4 min.

GLUCOPON 220UP: Reached 400 ml in 1.5 min, then retreated to 200 ml.

100 ppm Active: DUSTCON@: 2.3 min.

GLUCOPONo 425N: 2.7 min.

GLUCOPON'220UP: Reached 450 ml in 2.5 min, then retreated to 300 ml. d. Evaporation Rate Data The table below gives data from two sets of evaporation rate studies.

Both were done with haul road soil, screened to-30 mesh. Soil in a pan was spray-wetted to 15% moisture using aqueous solutions of surfactants at the indicated ppm actives level. Pans were allowed to dry in our 43% relative humidity atmosphere, and were weighed each hour. In the first set, five different conditions were scouted. In the second set, DUSTCON and GLUCOPONO 425N were compared at 50 ppm active in duplicate tests. As a measure of evaporation rate, the percent of total water loss (equilibrium) which is gone in two hours is given in the following table.

% of Total Water Loss Observed in Two Hours Surfactant-ppm active 1 st Set 2nd Set* DI water 75.9% 76.1% DUSTCONe-50 ppm 70.7% 72. 1% GLUCOPON#425N - 50 ppm 65.4% 68.1% GLUCOPON@ 425N-200 ppm 67. 1% GLUCOPON@ 220-50 ppm 66.5% * average of two determinations Total Water Loss as % of Initial Weight Surfactant-ppm active 1 st Set 2nd Set* DI water 13.9% 13.1% DUSTCON-50 ppm 13.5% 13.1 % GLUCOPONe 425N-50 ppm 12.8% 13.2% GLUCOPONs 425N-200 ppm 12.9% GLUCOPONs 220-50 ppm 13.3% * average of two determinations The time to reach 47g (roughly equivalent to about 3% moisture remaining in the soil) is: ppmSurfactant- active 2ndSetSet Water 2.0 hr 2.1 hr DUSTCONo-50 ppm 2.3 hr 2.4 hr GLUCOPON@ 425N-50 ppm 2.7 hr 2.5 hr