CPP — North Dry Ridge Recovery Methods

Technical report dated effective July 1, 2023, published February 26, 2024, describing the operating phosphate beneficiation plant at the Itafos Conda Project and a proposed modified flowsheet incorporating froth flotation to treat higher-MgO ore from the Husky 1/South Maybe Canyon deposits.

Report context

Section 17.0 of the NI 43-101 Technical Report for the Itafos Conda Project (Idaho, USA) describes the recovery methods for phosphate ore at the Conda Processing Plant (CPP). The report documents the existing Wash Plant flowsheet, its historical and recent operating performance, and a proposed plant modification designed to process higher-MgO ores from the Husky 1 and South Maybe Canyon (H1SMC) deposits. The existing Wash Plant was designed in the 1960s and processes phosphate ore from the RVM mine. The proposed modifications, prepared by JESA Technologies LLC, include a new flotation circuit to separate carbonate gangue minerals. All proposed modifications are presented as design criteria, not as constructed or operating facilities.

Processing route

Existing Wash Plant (current operations)

Phosphate ore is delivered to CPP by unit trains operating five days per week for 30 weeks (April to October), each train with a nominal payload of 13,300 tons (133 cars of 100 tons capacity each). Four ore qualities,Green, Blue, Red, and White,are received and stockpiled separately. Ore inventory at CPP typically ranges from 0.44 Mt to 1.54 Mt. Dozers reclaim and blend ore from stockpiles to feed the plant hopper. An 8-inch screen removes oversize material, which is returned to stockpiles, while the -8-inch material feeds the Wash Plant.

The average dry feed rate to the horizontal scrubber is 350 tph. The feed is mixed with recycled water from dewatering hydrocyclones to achieve 40%–50% solids and processed in a 10 ft x 12 ft horizontal scrubber that removes slimes, weak inclusions, and clay aggregates from phosphate mineral surfaces without liberating impure apatite. Scrubber discharge passes through a trommel with concentric 0.375-inch and 1.375-inch screens.

The -0.375-inch fraction proceeds to classification. The 1.375-inch x 0.375-inch material is sent to a rod mill. The +1.375-inch fraction (8-inch x 1.375-inch, about 20% of plant feed or 70 tph) is crushed in an open-circuit impact crusher, then combined with the 1.375-inch x 0.375-inch material and fed to an Allis Chalmers 9 ft x 12-ft rod mill loaded to 30%–35% volume with 4-inch diameter rods, operating at 64.8% of critical speed (16.56 rpm). The ore has a Bond Work Index of approximately 9.7 kwh/ton. Rod mill discharge is sized through a trommel with 0.375-inch and 1-inch openings. The +1-inch material is rejected; the 1-inch x 0.375-inch fraction returns as circulating load; the -0.375-inch fraction joins the primary -0.375-inch stream.

Under these grinding conditions, material finer than 325 mesh is limited to 5.5%–9.8% of the rod mill product. The combined -0.375-inch streams are pumped to a nest of five Krebs gMax-20 hydrocyclones (three operating, two standby) designed for a 325-mesh cut. The classification system achieved a relative efficiency of 90.23% (2018–2019 data) and an overall efficiency of 69.23%. Overflow constitutes final tailings (solids content 11.24%, 84.86% -325 mesh, representing 32.11% of feed weight). Underflow (0.375-inch x 325-mesh enriched phosphate ore) is dewatered using six Krebs D15B hydrocyclones (five operating, one standby) with 3-inch diameter apex and 6-inch diameter vortex finder, followed by two EIMCO Model 67 belt filters (extractors), one with a blower for cake drying. Filter cake moisture is 13.97%, representing the concentrate at 67.89% yield. Concentrate is stored in a bin or a 60,000-ton stockpile.

Concentrate is reclaimed and fed to two parallel FFE ball mills (11.5 ft x 21.5 ft each) using 2-inch diameter Cr-Mo steel balls, grinding to 98% passing 35 mesh for acceptable recovery in the phosphoric acid plant (PAP). Ground slurry is stored in an agitated tank for PAP feed.

The Wash Plant uses horizontal-centrifugal and vertical-centrifugal pumps and belt conveyors for materials handling. Tailings are pumped to the Tailings Pond by two horizontal centrifugal pumps (400 HP and 300 HP). The tailings pond dike is elevated by 1.6 ft per year; the maximum permitted elevation is 6,235 ft, 23 ft above the current elevation.

Proposed modified Wash Plant for H1SMC ores

The modified plant design, prepared by JESA Technologies LLC, divides processing into three sections: wash plant, flotation plant, and dewatering plant. Total phosphate ore feed is 375 tph. The plant is designed to operate in a new building with new equipment.

In the wash plant section, ore is fed via a new belt conveyor to an open-top surge hopper (1,357 ft³ capacity). A variable-speed scrubber belt feeder feeds a new horizontal rotary drum scrubber. Reclaim water maintains the correct solids percentage. Scrubber discharge reports to a trommel screen; oversize is cleaned with reclaim water and goes to a new Metso (Nordberg) NP20 impact crusher (168 tph capacity, 844 HP installed). Undersize and crusher product discharge onto a new inclined vibrating screen (Screen No. 1) making a 500 µm separation with reclaim wash water spray nozzles. The undersize (washed product) bypasses flotation entirely and goes directly to product de-sliming cyclones. The +500 µm oversize reports to a new rod mill (Metso-Outotec ball mill, 231 tph, 1,700 HP) operating in closed circuit with a second inclined vibrating screen (Screen No. 2). Screen No. 2 undersize goes to a classification cyclone tank; oversize returns to the mill. A new trommel screen on the mill rejects oversize to a bunker.

Classification uses new cyclones fed from the classification cyclone tank. Underflow gravitates to a coarse feed tank with agitator; coarse feed pumps send slurry to coarse dewatering cyclones (overflow returns to classification cyclone tank). Fine de-sliming pumps feed fine de-sliming cyclones; underflow gravitates to a fine feed tank with agitator; fine feed pumps send slurry to fine dewatering cyclones (overflow returns to fine de-sliming tank).

The flotation section comprises two separate circuits: coarse and fine. Coarse feed (from coarse dewatering cyclone underflow) enters a coarse pre-conditioner tank where dilute phosphoric acid is added (10% solution strength, consumption 0.76 lb/ton of rock). Slurry cascades to a coarse conditioner tank where collector is added (10% solution strength, consumption 1.65 lb/ton of rock), then flows to a coarse flotation column (Eriez HydroFloat). Plant air and flotation water assist flotation. Tails overflow from the top and gravitate to the tailings tank; concentrate discharges from the bottom to the coarse concentrate tank.

Fine feed undergoes the same conditioning sequence (phosphoric acid, then collector) and reports to fine flotation columns (Eriez column flotation cells). Tails overflow to the tailings tank; concentrate from the final column discharges to the fine concentrate tank. The flotation circuits are designed to float carbonate gangue (dolomite) away from phosphate minerals.

The dewatering section combines washed product, coarse concentrate, and fine concentrate in a product de-sliming tank. Product de-sliming pumps feed product de-sliming cyclones. Underflow gravitates to a product dewatering tank; pumps (new and existing) send slurry to product dewatering cyclones. Overflow goes to the tailings tank. Underflow gravitates to the existing extractor circuit. Dewatering cyclone overflow returns to the product de-sliming tank. A water collection tank receives filtrate, spray water, wash water, vacuum pump seal water, ball mill return water, reclaim water, and floor sump water; water collection pumps return water to the process.

• ### Three main plant sections
• Wash plant: scrubbing, crushing, screening, milling, and classification
• Flotation plant: coarse and fine conditioners, Eriez HydroFloat (coarse), Eriez column flotation cells (fine)
• Dewatering plant: de-sliming cyclones, dewatering cyclones, horizontal vacuum belt filters (extractors)

Key reported parameters

Technical qualifications

This profile summarizes the recovery methods described in Section 17.0 of the NI 43-101 Technical Report for the Itafos Conda Project, effective July 1, 2023, and published February 26, 2024. The existing Wash Plant is an operating facility; all metrics for the existing plant are based on historical and recent operating data (2018–2019 classification data referenced). The proposed modifications for H1SMC ores are presented as a Process Design Basis and Process Design Criteria prepared by JESA Technologies LLC; these are proposed designs, not constructed or operating facilities, and no modifications should be described as operational. The report includes measured metallurgical balance results (concentrate grade, tailings grade, and P₂O₅ recovery) from plant operation. No testwork results for the proposed flotation circuit are provided in the cited sections beyond equipment selection and design criteria. Flotation equipment capacities listed in Table 17.3 are design values; no demonstrated flotation recovery or concentrate grade for H1SMC ores is reported in the cited sections.

Source: NI 43-101 Technical Report, Itafos Conda Project, Idaho, USA, effective July 1, 2023, published February 26, 2024 (WSP USA Inc., Project 31405004.003). Section 17.0 Recovery Methods, subsections 17.1–17.5. of the original technical report.