2019 Itfos Conda Recovery Methods Technical Report

This technical report describes the recovery methods employed at the Conda Phosphate Plant Wash Plant in Soda Springs, Idaho, used to process RVM and LCM ores, along with proposed modifications for treating H1 and NDR ores.

Article Body

The Conda Phosphate Plant (CPP) Wash Plant is designed to process blended feed phosphate ore to meet the requirements of the CPP. The blended feed ore is first screened over an 8-inch screen (203,200 µm). The processing flowsheet involves horizontal scrubbing, sizing, crushing, rod milling, classification, and dewatering to produce a beneficiated phosphate concentrate suitable for downstream acid production.

Liberation of the impure fluor or hydroxy-apatite from contaminants requires grinding to -0.375 inch (-9,525 µm), as determined through mineral processing and metallurgical testing. The final sizing is achieved through rod milling and classification. In the classification stage, Krebs gMax-20 Hydrocyclones are utilized, with the overflow constituting the final tailings of the CPP. Of the hydrocyclones, five are in operation and one is on standby.

The process water demand, including raw/fire and potable/gland seal water, is estimated at 4,471 gpm. The material and water balance is shown in Figure 17-2 of the source report and presents average values for both materials and water.

Critical Data

Overview

The CPP Wash Plant processes RVM and LCM ores to meet the requirements of the CPP. The operation begins with screening over an 8-inch screen (203,200 µm). The blended feed undergoes size reduction in a rod mill, followed by classification using Krebs gMax-20 Hydrocyclones.

The performance of the CPP Wash Plant is documented in the metallurgical balance presented in Table 13-6 of the source report, covering the 2018-2019 operating period. The historical data indicates a P₂O₅ recovery of 81.18%, with rejection rates of 49.34% for MgO, 66.10% for Al₂O₃, 62.71% for Fe₂O₃, and 58.59% for SiO₂. These results are consistent with historical plant data from Agrium Nutrients and demonstrate that RVM and LCM phosphate ores do not present a risk to MAP, SPA, and APP production and quality.

Key Process Stages

Feed Screening and Crushing

The blended phosphate ore is screened over an 8-inch screen (203,200 µm). Material exceeding this size, the +8-inch fraction, is removed for further processing. The screening step ensures that the feed to downstream operations is appropriately sized.

Rod Mill Grinding

The 9-ft by 12-ft Allis Chalmers Rod Mill performs the primary grinding duty. For the proposed processing of H1 and NDR ores, the rod mill would be loaded with 4-inch diameter rods to avoid overgrinding. The ground product is then processed through a trommel equipped with two concentric screens of 0.375 inch (9,525 µm) and 1-inch (25,400 µm) openings. This arrangement produces minimum +1-inch rejects (+25,400 µm) and a 1 x 0.375-inch material (25,400 x 9,525 µm) fraction that returns to the rod mill for further grinding.

Classification and Dewatering

Classification is achieved using Krebs gMax-20 Hydrocyclones. The overflow of three operating hydrocyclones constitutes the final tailings of the CPP and is pumped to the Tailings Pond. The underflow, comprising 0.375-inch x 325-mesh material (9,525 x 44 µm), is expected to achieve the beneficiated product specifications.

Fine Flotation

For the processing of H1 ores, the flotation process is based on the Eriez Flotation Division/USA Final Report on Laboratory Testing. Characterization studies of the H1 Phosphate Ore were incorporated, and only relevant data from the Eriez report was considered. The flotation circuit includes Cav-Tube Flotation Columns. The 200 x 325-mesh material (75 x 44 µm) overflow is sent to fine flotation in columns, while the underflow comprising the 0.375-inch x 200-mesh size fraction (9,525 x 75 µm) that does not meet specifications is directed to a hydro separator.

Proposed Upgrades for H1 and NDR Ores

Characterization studies indicate that additional processing will be required to treat H1 and NDR ores. The proposed modifications include several unit operations. The screen assay data showed that impurities such as dolomite, aluminum silicates, clays, and silica tend to report to the -200-mesh size fraction (-75 µm), while P₂O₅ content decreases toward finer size fractions. Notably, only 7.12% of P₂O₅ content reports to the -200 mesh (-75 µm), while 32.52% of Al₂O₃, 14.2% of MgO, and 30.02% of SiO₂ report to this size fraction.

Downstream from the classification Krebs gMax-20 Hydrocyclones, additional hydrocyclones cutting at 200 mesh (75 µm) and a hydro separator at 48 mesh (300 µm) will process the ground material. The 48 x 200-mesh material (300 x 75 µm) is expected to fulfill the required product specifications. In the case that the +48-mesh material (+300 µm) is out of specifications, this size fraction will be ground in a ball mill to -48 mesh (-300 µm).

Estimated metallurgical results for the combined processing of the 28 x 200-mesh size fraction (300 x 75 µm) and flotation of the 200 x 325-mesh material (75 x 44 µm) indicate a beneficiated product at specifications of 30.41% P₂O₅ with 1.05% Al₂O₃. However, initial characterization results were not close to the desired specifications, indicating that contaminants trended to be reported in the -325-mesh fraction.

Additional Interesting Data and Summary

The CAPEX cost estimate for the proposed modifications varies depending on the final pieces of equipment to be added to the Wash Plant. The major cost components include the ball mill for 250 tph of -48 mesh product at US$5,500,000 (installation and accessories included), scrubbing equipment at US$650,000, Cav-Tube Flotation Columns at US$650,000, and a hydro separator cutting at 48 mesh at US$515,000. Additional costs include sump and pump systems at US$250,000, dewatering hydrocyclones at US$125,000, hydrocyclones cutting at 200 mesh at US$125,000, and piping, connection, cabling, and switches at US$200,000. The total estimated CAPEX is US$10,180,000.

The modifications are expected to include grinding in a ball mill of the +48 mesh (+300 µm) material. Based on the results of characterization studies, a final-defined flowsheet and new operating conditions will be established.

Key Processes

• Horizontal scrubbing of blended phosphate ore
• 8-inch (203,200 µm) feed screening
• Rod mill grinding to -0.375 inch (-9,525 µm) for liberation
• Krebs gMax-20 Hydrocyclone classification
• Dewatering stages
• Column flotation using Cav-Tube Flotation Columns
• Ball mill grinding for +48 mesh (+300 µm) oversize material
• Hydro separator cutting at 48 mesh (300 µm)
• Hydrocyclones cutting at 200 mesh (75 µm) for fine classification

Source: 2019 Itfos Conda Recovery Methods Technical Report, December 2019.

Project website: 2019 Itfos Conda Recovery Methods Technical Report