Process and chemistry for reducing dolomite concentrations in phosphate processing

Abstract

A magnesium suppressant/flocculant for use in separating dolomite from calcium phosphate. The magnesium suppressant/flocculant may be applied at a mine site prior to subjecting ore fractions to phosphate flotation or at a chemical plant after grinding.

Claims

1. A method of reducing dolomite concentrations in phosphate processing, the method comprising: adding a magnesium suppressant to phosphate-containing fractions; conditioning the fractions with fatty acid; and subjecting the fractions to a phosphate flotation; where the magnesium suppressant is a polymer comprising: a base monomer comprising acrylic acid, acrylamide, or a combination of acrylic acid and acrylamide; and a functional monomer comprising hydroxyl ethyl methacrylate, 2-acrylamido-2-methyl propane sulfonic acid, 3-allyloxy-1, 2-propanediol, and/or a derivative thereof.

2. The method of claim 1 where adding the magnesium suppressant to the fractions prevents magnesium within the fractions from interacting with the fatty acid, which minimizes the extent to which the magnesium interacts with hydrophobic bubbles during the phosphate flotation.

3. The method of claim 1 further comprising grinding the fractions prior to adding the magnesium suppressant.

4. The method of claim 3 where the grinding results in a particle size of less than 100 microns.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The devices and methods discussed herein are merely illustrative of specific manners in which to make and use this invention and are not to be interpreted as limiting in scope.

(2) While the devices and methods have been described with a certain degree of particularity, it is to be noted that many modifications may be made in the details of the construction and the arrangement of the devices and components without departing from the spirit and scope of this disclosure. It is understood that the devices and methods are not limited to the embodiments set forth herein for purposes of exemplification.

(3) In general, in a first aspect, the invention relates to a process and chemistry for reducing dolomite concentrations in phosphate processing.

(4) As discussed above, the typical process for removing phosphate from ore at a mine site involves a four stage process. First, the ore may go through various washing and screening stages to remove large, high quality phosphate rock. Second, the remaining fractions may be washed, deslimed, and put through a hydrocyclone to reduce clays and silica. Third, the remaining fractions, which are typically between 100 and 1000 microns, may be subjected to a phosphate flotation using fatty acid collectors. Fourth, the remaining fractions may be subjected to a reverse flotation process where the sand is floated with an amine and the phosphate stays behind. The phosphate may then move on to a dewatering step before being transferred or sold to a fertilizer production chemical plant.

(5) In a first embodiment, the process for reducing dolomite concentrations may involve adding a step prior to step 3, the first flotation step. Prior to conditioning the phosphate slurry or rock with fatty acid before entering the rougher float cell, a magnesium suppressant may be added. The magnesium suppressant may selectively complex with the magnesium, which may prevent or minimize the magnesium from interacting with the fatty acid, thus minimizing its interaction with the hydrophobic bubbles, which is what removes the phosphate. Essentially, by complexing with the magnesium carbonate, the magnesium suppressant may inhibit the magnesium carbonate from complexing with the fatty acid that would generally make it float due to the similar chemical characteristics to the desired calcium phosphate.

(6) Further improvement may be found by grinding the material prior to adding the magnesium suppressant, as discussed above. The grinding may occur through pipe sheering during transportation or through an external mechanical source, such as a ball mill. The smaller particle size may make the magnesium more liberated and thus easier to complex. The grinding may result in a particle size of less than 100 microns.

(7) In a second embodiment, the process for reducing dolomite concentrations may occur at the chemical plant. During processing, the phosphate rock may be transferred into a clarifier or thickener. During this step, the magnesium suppressant may be added to selectively flocculate the dolomite from the calcium phosphate. The dolomite may then settle to the bottom of the thickener or clarifier and be removed from the bottom and transferred to a tailings pond while the calcium phosphate is separated. Alternately, the phosphate product entering the chemical plant may be rinsed with pond water, which may extract much of the magnesium as soluble magnesium. The calcium phosphate may be filtered or removed by some other means. The now magnesium enriched water may then be treated with either the magnesium suppressant or a combination or coagulant and magnesium suppressant. In both in-plant options, the magnesium suppressant should complex with the magnesium carbonate preferentially over calcium phosphate and settle, thus separating from the calcium phosphate.

(8) As with the first embodiment, further improvement may be found by decreasing the size of the material prior to adding the magnesium suppressant. Once the product reaches the chemical plant, a size reduction may be required and may occur in a ball mill. This is often necessary for adequate dissolution and acidification during the fertilizer production. During the grinding, not only is the calcium phosphate ground smaller for the required processing, but the dolomite is also ground smaller. This may be beneficial for the application of the present invention. The smaller particle size may make the magnesium more liberated and thus easier to complex. The grinding may result in a particle size of less than 100 microns.

(9) The magnesium suppressant may be a polymer. In particular, the magnesium suppressant may be at least a copolymer if not a tertpolymer. The base chemistry may be acrylic acid, acrylamide, or a combination of acrylic acid and acrylamide. The functionality for the magnesium complexation may come from adding one or more of the following monomers to the polymer: hydroxyl ethyl methacrylate, 2-acrylamido-2-methyl propane sulfonic acid, 3-allyloxy-1, 2-propanediol, and/or a derivative thereof. When used during the flotation stage, the molecular weight of the polymer may be from around 3,000 daltons to 30,000 daltons, but may go as high as 500,000 daltons. When used at the chemical plant, the molecular weight of the polymer may be from around 200,000 daltons to millions of daltons, but may go as low as 20,000 daltons. The charge of the functionalized monomer may be around 10% to 30%, but could be higher or lower.

(10) Whereas, the devices and methods have been described in relation to the drawings and claims, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention.