Beneficiation Of Phosphate Ores Research Articles

(Invited) Process for Continuous Electro-Osmotic Dewatering of Phosphatic Clay Suspensions

A recent spill of wastewater at a former phosphate mining facility in Piney Point Florida, reported in March 2021, highlights the need for alternatives to creating large impoundments of the dilute 2-3 wt.% suspension of phosphatic clay produced as a waste stream in the beneficiation of phosphate ore. A 1997 report highlights releases in Florida.1 In 1994, the earthen berm of a clay settling area operated by Hopewell Mine failed along a section of approximately 100 feet. Approximately 482 million gallons of water were lost. A series of releases of large volumes of turbid water from clay settling areas into nearby surface waters occurred between 1989 and 1993 at the MMM Nichols Phosphate Mine. In 1994, the dike of an inactive settling area was breached over a section of approximately 150 linear feet, causing very rapid dewatering of the impoundment.A typical Florida phosphate mining operation produces more than 6,300 L/s of phosphatic clay. The clay-water suspension is pumped into large impoundments called clay settling areas in which separation is achieved by hindered settling and self-consolidation. As it settles, the supernatant water is recycled for use in the beneficiation plant. A top crust is formed after a few years, but the clay beneath the crust has a large water content and a pseudo-plastic character that limits the amount of weight the settling area can support. Clay settling areas cover roughly 390 square kilometers of land in Florida. Uses for the land are limited by the properties of the clay that leave the settling areas unstable, even after 50 years of elapsed time.This presentation will describe the results of a research project, funded by Mosaic, to create an electrokinetic alternative to creation of clay settling areas. Research in use of electrokinetic phenomena to accelerate the dewatering process has been active for more than 50 years.2 The use of an electric field to separate the water from the solids is attractive because the inherent stability of the clay suspension is due, in part, to the surface charges residing on the platelets. A single-stage design was developed for continuous electro-osmotic dewatering of phosphatic clay suspensions that demonstrated efficient production of a dewatered cake with a solids content of 35 wt.% at a dry-clay production rate of 4.5 kg/h m2 from a feed clay of 10 wt.%.3,4 The results were supported by measurements of yield stress and a mathematical model that accounted for compressibility of the cake and for both electro-osmotic and hydraulic permeability.5 References Damage Cases and Environmental Releases from Mines and Mineral Processing Sites, U.S. Environmental Protection Agency, Washington, DC, 1997.Dizon and M. E. Orazem, "Advances and Challenges of Electrokinetic Dewatering of Clays and Soils," Current Opinion in Electrochemistry, 22 (2020), 17-24.Kong, A. Dizon, S. Moghaddam, and M. E. Orazem, “Development of Fully-Continuous Electrokinetic Dewatering of Phosphatic Clay Suspensions,” in Electrochemical Engineering: From Discovery to Product, Volume XVIII of Advances in Electrochemical Science and Engineering, R. Alkire, P. N. Bartlett, and M. Koper, editors, John Wiley & Sons, Hoboken, 2018, 159-192.Dizon and M. E. Orazem, “Efficient Continuous Electrokinetic Dewatering of Phosphatic Clay Suspensions,” Electrochimica Acta, 298 (2018), 134-141.Dizon and M. E. Orazem, “Mathematical Model and Optimization of Continuous Electro-Osmotic Dewatering,” Electrochimica Acta, 304 (2019) 42-53.

Enhanced leaching recovery of rare earth elements from a phosphatic waste clay through calcination pretreatment

Phosphatic clay is a waste material produced during the beneficiation of phosphate ore, which likely poses severe environmental problems. In this study, a phosphatic clay containing 258 ppm of total rare earth elements (REEs) was used as a feedstock for REE recovery. By reacting with 0.1 M HCl at 75 °C for 3 h, around 36 % of light REEs and 65 % of heavy REEs were extracted from the raw material. However, after calcination pretreatment at 600 °C for 2 h, the recovery was increased to 73 % and 81 %, respectively, which are close to the recoveries obtained from the raw material using a much higher acid concentration of 1.2 M. Based on the findings from sequential chemical extraction tests and scanning electron microscopy analysis, the positive impact was explained by the decomposition and conversion of REE-bearing minerals into more leachable species. Using a higher calcination temperature of 900 °C, recovery of both the light and heavy REEs was largely reduced relative to the raw material. Mineralogical analyses showed that the dominant minerals existing in the material, such as muscovite, were fused and sintered during the calcination at 900 °C. These reactions likely caused the decreases in the recovery. The results and findings from this study will contribute to the beneficial uses of phosphatic clay and the production of REEs.

Mathematical Model and Optimization of Continuous Electro-Osmotic Dewatering

A dilute 2-3 wt.% suspension of phosphatic clay is produced as a waste stream in the beneficiation of phosphate ore. A typical Florida phosphate mining operation produces more than 6,300 L/s of phosphatic clay. The clay-water suspension is pumped into large impoundments called clay settling areas in which separation is achieved by hindered settling and self-consolidation. As it settles, the supernatant water is recycled for use in the beneficiation plant. A top crust is formed after a few years, but the clay beneath the crust has a large water content and a pseudo-plastic character that limits the amount of weight the settling area can support. Uses for the land are limited by the properties of the clay that leave the settling areas unstable, even after 50 years of elapsed time.1 The objective of the present work was to develop a mathematical model based on soil mechanics, electrokinetic phenomena, and transport phenomena that describes a fully continuous electrokinetic dewatering apparatus for processing a dilute phosphatic clay to a dewatered plastic cake. The physical system studied is based on a prototype developed by Dizon and Orazem.2 A constrained optimization strategy was developed that yielded the process parameters of a cost-optimized continuous electrokinetic dewatering process and was used to simulate an industrial-scale operation.3 The model developed in this work adequately represented experimental data collected for the operation of the lab-scale continuous electrokinetic dewatering prototype. The optimization strategy consisted of a constrained maximum electric field and final solids content of 35 wt% for a continuous electrokinetic dewatering process starting with a feed clay with a solids content of 10 w%. Optimal operating parameters were identified for an industrial-scale continuous electrokinetic dewatering process capable of processing the effluent production rate of the Mosaic Co. Four Corners Mine. The simulation results suggest that lower total costs may be achieved with small electrode gaps. The cost-optimized process parameters were a feed-side gap of 8.5 cm, a residence time of 1.3 hours, and a dry-clay production rate of 7.58 kg/h m2. An estimated total electrode area of 0.17 km2 was required. The total cost of an optimized industrial-scale continuous electrokinetic dewatering process was estimated to be $9.12 per metric ton of dry clay. References Kong, A. Dizon, S. Moghaddam, and M. E. Orazem, “Development of Fully-Continuous Electrokinetic Dewatering of Phosphatic Clay Suspensions,” in Electrochemical Engineering: From Discovery to Product, Volume XVIII of Advances in Electrochemical Science and Engineering, R. Alkire, P. N. Bartlett, and M. Koper, editors, John Wiley & Sons, Hoboken, 2018, 159-192.Dizon and M. E. Orazem, “Efficient Continuous Electrokinetic Dewatering of Phosphatic Clay Suspensions,” Electrochimica Acta, 298 (2018), 134-141.Dizon and M. E. Orazem, “Mathematical Model and Optimization of Continuous Electro-Osmotic Dewatering,” Electrochimica Acta, 304 (2019) 42-53.

Progress in the Development of Prototypes for Phosphatic Clay Electrokinetic Dewatering

A dilute 2-3 wt.% suspension of phosphatic clay is produced as a waste stream in the beneficiation of phosphate ore. A typical Florida phosphate mining operation produces more than 100,000 gallons/min of phosphatic clay. The suspensions are pumped into large impoundments called clay settling areas (CSA) in which separation is achieved by hindered settling and self-consolidation. As it settles, the supernatant water is recycled for use in the beneficiation plant. A top crust is formed after a few years, but the clay beneath the crust has a large water content and a pseudo-plastic character that limits the amount of weight the settling area can support. As much as 25 -50 years are needed to reach a solids content greater than 25 wt.%. Clay settling areas cover about 30-40% of the mined land. Uses for the land are limited by the properties of the clay that leave the settling areas unstable. Methods that employ electrokinetic phenomena have been the subject of significant research as a possible means of accelerating the dewatering process. Previous research to develop batch electrokinetic dewatering processes resulted in the determination that the electrokinetic dewatering was not economically feasible. The objective of our work was to overcome the economic hurdle through the development of continuous electrokinetic dewatering (EKD). The previous continuous design was a single unit in which a cake was formed in the horizontal section and the cake was dewatered in the slanted section. Separation of the single-unit process into two units yielded greater throughput, but the projected cost per metric ton of dry clay was not substantially lower than that of the previous prototype. The latest prototype consists of a single unit which accepts a 10 wt.% suspension as a feed and produces up to a 38 wt.% cake. As compared to our previous prototype, the new unit has improved the viability of industrial EKD by reducing both capital and operational cost through increased throughput, reduced materials cost, and improved clay-water separation efficiency.

(Invited) Electrokinetic Separations to Increase the Percent Solids of the Effluent from a Phosphate Mine

Phosphate mining operations create a waste product, consisting of a dilute clay/sand/phosphate suspension that, due to the properties of the suspended solids (primarily clay), requires 25 to 50 years to densify via hindered settling and self-weight consolidation. The objective of this research was to develop and apply an effective electrokinetic separation process to phosphatic clay suspensions, generated during the beneficiation of phosphate ore, a major component of fertilizer. The use of an electric field to separate the water from the solids is attractive because the inherent stability of the clay suspension is due, in part, to the surface charges residing on the platelets.Previous work by others has demonstrated the feasibility of batch-wise electrokinetic separation of phosphatic clay suspensions, but the process is widely regarded as uneconomical. The present research is predicated on the assumption that an economically feasible separation requires a continuous, electrokinetic separation procedure.Solid-liquid separation represents a significant problem for the phosphate mining industry The waste suspensions, initially containing 3-5 wt% solids, are pumped to large impoundment areas termed clay settling ponds. When incorporated, the addition of flocculating agents produce a rapid, but partial, separation, to approximately 10 wt% solids. A further increase in solids content proceeds very slowly. Hindered settling, followed by self-weight consolidation, requires as much as 25 years to reach a solids content of 40 wt%. This is an important target value, because its shear strength will then allow the addition of a surcharge (typically a sand cap) to increase the consolidation rate and magnitude. Through a systematic development of prototypes, from batch to semi-continuous with emphasis on water clarification to semi-continuous with emphasis on solids extraction, our team has developed a fully continuous electrokinetic dewatering prototype. The system takes advantage of the charged nature of the suspended solids. When subjected to an applied electric field, the solids are attracted to the anode and clarified water is collected at the cathode. The process is capable of generating a 40 wt% clay cake and clarified water with turbidity levels below 1 NTU within hours rather than years. Optimization of the design was possible by developing a constitutive relationship between the final solids content, the applied electric field, and the residence time. Successful implementation of a continuous electrokinetic separation process will reduce the vast amount of water consumed by industry. While the process was developed for phosphatic clay suspensions, it is anticipated that electrokinetic dewatering may be applicable to other mining operations such as those associated with the oil sand tar tailings in Canada. This presentation will describe the current state of development, including energy and power requirements.

The effect of jojoba oil on the surface properties of calcite and apatite aiming at their selective flotation

The beneficiation of phosphate ores by froth flotation is the most efficient process used to separate apatite from calcium minerals. However, the similarity of surface properties between apatite and calcite generally leads to non-selective adsorption of reagents, rendering the selective separation of these minerals a problem, demanding a specific approach. The sedimentary phosphate deposit of Itataia, Brazil, studied in this paper, presents a complex mineralogical composition. The bulk flotation of apatite and calcite with anionic collectors in an alkaline medium followed by selective flotation of calcite at pH5.5 using phosphoric acid or citric acid as depressant has been suggested for this ore. In the present work, contact angle measurements were performed to evaluate the behavior of jojoba oil as an alternative collector for the selective separation of apatite and calcite minerals. Jojoba oil is composed mainly of gondoic, erucic and oleic acids. The hydrophobicity studies were undertaken using a computer controlled contact angle goniometer. Additionally, the collector adsorption was evaluated through electrophoretic mobility and FTIR measurements. The results indicated that a high selectivity between calcite and apatite can be obtained by using jojoba oil as a collector at slightly acid medium, without the use of depressants. The most interesting results were achieved with a jojoba oil concentration of 200mg·L−1 at pH6.5, where the apatite was fully hydrophilic while calcite showed high hydrophobicity.

ChemInform Abstract: A Review of the Beneficiation of Calcareous Phosphate Ores Using Organic Acid Leaching

AbstractReview: 159 refs.

A review of the beneficiation of calcareous phosphate ores using organic acid leaching

Abstract The beneficiation of phosphate ores containing carbonate gangue by conventional techniques such as physical separation methods or flotation is very difficult due to the similarities in physico-chemical properties of constituent minerals present in the system. Carbonate-rich phosphate deposits can be processed by calcination and by selective acid leaching methods. However, calcination has some drawbacks and selective leaching with organic acids is a promising method for the beneficiation of this type of ore. In this paper, the leaching of calcareous phosphate ores proposed in the literature is reviewed with the aim of identifying the important factors involved in the dissolution process. The literature indicates that the organic acid reagent, acid concentration, reaction time, solid/liquid ratio, temperature, particle size distribution and stirring speed are important parameters in the process. The range and optimum values of these parameters reported in the literature are summarized, but there is still some doubt regarding the optimum reaction time. Analysis of the leaching kinetic data and activation energy show that the leaching reaction is chemically controlled. Limited consideration is given to the economic aspects of organic acid leaching. The leaching method appears to be cheap, but a complete economic evaluation is required for each ore, dependent upon the local price of the organic acids used and the cost of their recovery. It is proposed that future research should focus on the leaching characteristics of specific calcareous phosphate ores and on the development of a methodology to optimise leaching using organic acids.

Separation of Valuable Fine Phosphate Particles from Their Slimes by Column Flotation

Large quantities of fines are generated as slimes during beneficiation of phosphate ores. These slimes are discarded due to the lack of a suitable method for their treatment. This decreases the total recovery of phosphate. Moreover, the presence of these slimes causes an environmental problem in some localities. This paper studies the possibility of recovering the valuable fine phosphate particles (45 μm) from their slimes through the application of the column flotation technique. Tests were performed using oleic acid as a collector for the phosphate minerals, and sodium silicate as a depressant for their associated gangues. The main operating parameters affecting the performance of column flotation were investigated. The results indicate that the best operating conditions for column flotation of phosphate slimes are: superficial gas velocity 0.84 cm/s, frother concentration 0.1 kg/ton, column height 230.5 cm, and superficial water velocity 2.2 cm/s. At these conditions a product assaying 25.3% P2O5 (∼55.24% BPL, bone phosphate of lime) and 14.64% I.R. (insoluble residue) with a P2O5 recovery of about 51.52% was obtained from a feed containing 18.26% P2O5 (∼39.87% BPL) and 24.03% I.R. Such a grade and recovery were not obtained by applying the conventional froth flotation technique, even after cleaning the rougher concentrate. Recovery of more than 50% of phosphate from disposed slimes will improve the economic viability of the beneficiation process for phosphate ores. It will also help in solving the environmental problems associated with the disposal of these slimes.

Beneficiation of phosphate ores using high gradient magnetic separation

Phosphate ores from Rajasthan and Madhya Pradesh were subjected to two-stage high gradient magnetic separation using magnetic coating with magnetite and sodium oleate. Dipotassium hydrogen phosphate was used to prevent the coating of magnetite on phosphate in the first stage whereas sodium metasilicate was used to prevent the coating on silica in the second stage. The results indicate that HGMS combined with an appropriate reagent scheme to condition the mineral surfaces results in selectivity.

Glass facing materials based on the waste from the beneficiation of phosphate ores

The authors study the feasibility of obtaining phosphate glass facing materials from the flotation and washing tailings created during the enrichment of phosphate ores. A variety of chemical compositions are synthesized and tested with the intent of optimizing a number of properties including corrosion resistance in acidic media, thermal expansion coefficients, flexural and compression and impact strength, heat resistance, and wearability.

A factor analysis study of phosphate beneficiation by calcination

Mineralogical changes during beneficiation of phosphate ore by calcination and washing were studied by factor analysis with oblique rotation, and by using factors of factors (obtained with a factor—factor correlation matrix as input). Several minerals and reactions are indicated, including the possibility of distinguishing between different contributions to the CO 2 variance. From the point of view of using the results as a guide for multiregression analysis and building a linear model for the process, the most important results are as follows. The parameters of the product grade (P 2O 5 and chloride) are influenced by factors measured by x-ray fluorescence (Al 2O 3, SiO 2 SO 3 and MgO). Factors measured by thermogravimetry (water of hydration, portlandite and carbonate) have only a small influence. Most of the variance for halite is determined by elements derived from clay, whereas most of the variance for CO 2 is correlated with MgO. Magnesium replacing calcium in the francolite indicates the CO 2 level and thus the decrease in P 2O 5 content. The MgO content in the francolite can be used to indicate the maximum P 2O 5 content in the product.