Patent Grant
6994786
The present invention relates to a phosphate ore beneficiation process, which includes a more ecologically acceptable replacement for the petroleum based fuel or reclaimed oil commonly used as part of the primary collection process.
Apatite is the name applied to a group of calcium phosphate minerals containing other elements or radicals. The mineral occurs in the United States mainly in the form of the calcium phosphate ores that are referred to generically as phosphate rock. Phosphate rock is rock that consists of calcium phosphate largely in the form of the aforementioned apatite together with clay, quartz, and other non-valuable minerals, and is useful in fertilizers and as a source of phosphorus compounds. It occurs in large beds in the southeastern and the northwestern U.S.
The calcium phosphate is normally separated from other constituents of the ore by froth flotation. The de-slimed and sized calcium phosphate is floated from a slurry by aeration with the aid of one or more flotation agents. Most widely used flotation agents/collectors are the unsaturated fatty acids, for example, oleic acid, and the technical grades or commercial grades of naturally-occurring fatty acid mixtures having a high proportion of unsaturated fatty acids derived from such oils as such as tall oil, corn oil, safflower oil, soybean oil, cottonseed oil, and linseed oil, and derivatives thereof, as well as synthetic acids. The flotation effect of the fatty acids is usually enhanced by mixing in a similar amount of a petroleum-based hydrocarbon, such as diesel oil, #5 fuel oil, or reclaimed oil, which sometimes contains a small amount of a nonionic or anionic emulsifier. The use of such petroleum-based hydrocarbons is causing concern because eventually part of the process water and all of the flotation “tailings” are returned to the environment whereby the petroleum hydrocarbons could enter waterways and aquifers. Unlike the fatty acid based components, fuel oil and reclaimed oils may contain fractions that are non-biodegradable and can contain hazardous polynuclear aromatics.
It has been found that the petroleum-based hydrocarbons can be replaced by methyl and/or ethyl esters of fatty acids without adversely effecting the flotation process. Such esters are produced from animal and vegetable renewable resources and are readily biodegraded. Specifically, the ester substitution is more fully described below.
More specifically, the present invention is a process for use in a phosphate ore beneficiation process. It is a method for minimizing the long-term environmental impact of the use of petroleum-based hydrocarbon materials mixed with fatty acid based anionic flotation reagents for froth flotation in the flotation of phosphate ores, and comprises substituting said petroleum based hydrocarbon materials with methyl and/or ethyl esters of fatty acids.
The esters of fatty acids are derived from:
The methyl or ethyl esters and combinations thereof are derived from animal, plant and synthetic materials esters.
When the fatty acid is a crude tall oil and residual rosin acids interfere with the flotation process, the residual rosin acids remaining after esterification are reacted with an alkaline earth base in stoichiometric quantities to neutralize the acid.
When an increase in viscosity occurring by the neutralization process is undesirable, a desired proportion of non-crude tall oil derived methyl or ethyl ester is added to reduce the viscosity to an acceptable level.
The methyl and/or ethyl esters are blended with the fatty acid based primary floatation reagents in a proportional ratio of from about 25:75 to 75:25.
The blended esters and reagents are added to a deslimed and sized phosphate rock slurry at a level normally about 0.3 to 3.0 pounds per ton of dry feed.
This disclosure describes the use of methyl and/or ethyl fatty acid esters as a component of anionic flotation reagents to replace petroleum derived hydrocarbons such as diesel oil, #5 fuel oil or reclaimed oil.
The methyl and/or ethyl esters useful in the present invention can be prepared by methods known in the art whereby the appropriate alcohol is reacted with an oil such as rapeseed, sunflower, corn, safflower, and soybean, fatty acids obtained from these oils, or tall oil derived fatty acids including heads and crude tall oil.
In the event that a crude tall oil is the source of the fatty acids, it is difficult to react the rosin acids to completion within a reasonable time or without using extreme conditions of temperature and pressure. It has been found that such residual rosin acids interfere with the flotation process and as an alternative to driving the reaction to near completion by the methods described above, can be effectively neutralized by the addition of a stoichiometric amount of calcium oxide or hydroxide. The resultant increase in viscosity by this reaction may also be undesirable in some cases so a proportion of a non-crude tall oil derived methyl or ethyl ester can be added to reduce the viscosity to a more acceptable level.
The esters described in this patent are blended with the fatty acid based anionic flotation reagent in a proportion from 25:75 to 75:25 and added to the deslimed and sized phosphate rock slurry at a level normally about 0.3 to 3.0 pounds per ton of dry feed.
The effectiveness of flotation reagents can be demonstrated in the laboratory by the use of a scaled down flotation cell to simulate full-scale production unit conditions.
A sample of the methyl ester of soybean fatty acids (biodiesel) was obtained from World Energy. The acid value was 0.07 mg KOH/g. This was mixed with a commercial fatty acid flotation reagent Custofloat 20 manufactured by Arr-Maz Custom Chemicals in the proportion 75:25 fatty acid:ester. A similar formulation replacing the ester with #5 fuel oil was prepared for comparison purposes.
Flotation experiments were conducted in a 3-liter Denver cell using feed obtained from Central Florida phosphate mine 1. A sample of about 700 g feed, accurately weighed, was first conditioned at 70% solids with 0.20 g (equivalent to 0.59 pounds/ton of feed) of the formulated flotation reagent for 90 seconds at 900 rpm. The sample was then diluted to 20% solids and floated at 1500 rpm for 60 seconds. The froth product and the flotation tailings were dried, weighed, and analyzed for P2O5 content by a spectroscopic method. Results were expressed as BPL (bone phosphate lime).
A methyl ester of tall oil heads was prepared by refluxing an excess of methanol with a tall oil heads of acid value 141.7 mg KOH/g using an acid catalyst. The product was separated, washed, and dried and had a final acid value of 4.5 mg KOH/g. This was mixed with a commercial fatty acid flotation reagent Custofloat 18G manufactured by Arr-Maz Custom Chemicals in the proportion 60:40 fatty acid:ester. A similar formulation replacing the ester with #5 fuel oil was prepared for comparison purposes.
Flotation experiments were conducted in a 3-liter Denver cell using feed obtained from Central Florida phosphate mine 2. A sample of about 700 g feed, accurately weighed, was first conditioned at 70% solids with 0.40 g (equivalent to 0.75 pounds/ton of feed) of the formulated flotation reagent for 90 seconds at 900 rpm. The sample was then diluted to 20% solids and floated at 1500 rpm for 60 seconds. The froth product and the flotation tailings were dried, weighed, and analyzed for P2O5 content by a spectroscopic method. Results were expressed as BPL (bone phosphate lime).
A methyl ester of crude tall oil was prepared by refluxing an excess of methanol with a crude tall oil of acid value 123.5 mg KOH/g using an acid catalyst. The product was separated, washed, and dried and had a final acid value of 55.0 mg KOH/g. The ester was heated to 230° F. and sufficient CaO added to yield an essentially neutral product. The rather viscous product was mixed with the tall oil heads ester in Example 2 in the proportion of 75 to 25 parts by weight to yield a product having a similar viscosity to #5 fuel oil. This was mixed with a commercial fatty acid flotation reagent Custofloat 18G manufactured by Arr-Maz Custom Chemicals in the proportion 60:40 fatty acid:ester. A similar formulation replacing the ester with #5 fuel oil was prepared for comparison purposes.
Flotation experiments were conducted in a 3-liter Denver cell using feed obtained from Central Florida phosphate mine 3. A sample of about 700 g feed, accurately weighed, was first conditioned at 70% solids with 0.49 gm (equivalent to 1.4 pounds/ton of feed) of the formulated flotation reagent for 90 seconds at 900 rpm. The sample was then diluted to 20% solids and floated at 1500 rpm for 60 seconds. The froth product and the flotation tailings were dried, weighed, and analyzed for P2O5 content by a spectroscopic method. Results were expressed as BPL (bone phosphate lime).
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