Rare Earth Separation Cases: Transport Protection for Mixer-Settlers & Centrifugal Extractors

Maintenance in a rare earth separation plant starts with an unavoidable premise: the moment any unit is opened, what comes out is acidic organic phase, fluoride-bearing complexes, and traces of associated thorium and uranium. The mixing chamber lifted from a mixer-settler still carries a mix of P507 and kerosene; the drum of a centrifugal extractor still holds un-drained aqueous phase; an online analysis probe has just been pulled out of a hydrochloric acid circuit. These parts are sensitive to impact and scratches, they corrode further when residue absorbs moisture, and they add a compliance dimension that is easy to overlook.

JUNZHIJIA holds one principle: for rare earth separation equipment, first separate the aqueous, organic and solid residues, then work backward from acidity, radioactivity and precision surfaces to case structure. General chemical packaging experience solves only half the problem here; the other half belongs to residue control, compliance marking and leakage prevention. This article follows the solvent extraction main line stage by stage and gives deployable solutions, comparison tables and acceptance criteria.

Table of Contents

• Rare Earth Separation Process Chain and Protection Challenges
• Mixer-Settler (Extraction Box) Parts
• Centrifugal Extractors and Extraction Column Parts
• Pumps, Valves and Flow Control Parts
• Materials and Corrosion Control in Acidic Organic Media
• Compliance and Protection for Radioactive Associated Materials
• Case Shell Materials and Structural Design
• Sealing Classes: IP65 / IP67 with IEC 60529 and GB/T 4208
• Cushioning and Compartmentalized Liner Options
• Latches, Hinges, Pressure Equalization Valves and Stacking Load
• Temperature, Humidity, Salt Spray and Transport Testing
• Customization, OEM/ODM and Acceptance Criteria
• Frequently Asked Questions FAQ
• Conclusion and Related Reading

Rare Earth Separation Process Chain and Protection Challenges

Rare earth elements have extremely similar chemistry, so industry separates them mainly by solvent extraction through many stages. A typical separation line runs: feed preparation and impurity removal, saponification and extractant make-up, multi-stage extraction in mixer-settlers or centrifugal extractors, stripping and precipitation, then calcination to oxide. The core separation equipment is the extraction box, or mixer-settler, and the centrifugal extractor, and together they carry most of the mass transfer and phase separation duty.

Four constraints dominate when these units are shipped for maintenance, plant relocation or spare-part transfer:

Unlike ordinary chemical parts, rare earth separation parts often carry acid and organic solvent at the same time. The acidic aqueous phase creates an electrochemical corrosion environment on metal, while the organic phase swells rubber and plastic parts; combined, they accelerate seal and lining failure. Protection design therefore has to begin with residue removal, not with choosing a case.

Mixer-Settler (Extraction Box) Parts

A mixer-settler comprises a mixing chamber and a settler chamber, cascaded over many stages. Parts lifted during maintenance include agitators and shafts, mixing chamber baffles, settler dividers and weir plates, interstage connecting pipes, anti-vortex baffles and interface control devices.

Mixer-settler parts are usually a combination of thin plates and long shafts, so shafts and plates should be separated into different compartments. A shaft is governed by straightness; a plate is governed by flatness and edge integrity, and their support logic is opposite — a shaft must be cradled at multiple points so it cannot bend, while a plate must be clamped across its whole face so it cannot curl. If plates must be stacked, insert PE separators between layers and bundle the stack so that it cannot shift and rub. Interstage pipes and interface parts belong in their own slots with capped ends, separated by removable dividers. Where a part has an acrylic or PVDF sight window, that face should point upward or inward and must never take direct load.

Centrifugal Extractors and Extraction Column Parts

Centrifugal extractors separate phases by high-speed rotation, which is efficient but mechanically demanding; extraction columns achieve multi-stage mass transfer with internals such as sieve plates, packing and pulse generators. Their transport risks differ sharply.

Centrifugal extractors. Shippable parts include the drum assembly, main shaft, bearing housings, casing, inlet and outlet piping and couplings. The drum is the critical item: it requires balancing accuracy, and any impact, slight distortion or journal scratch is amplified into vibration at speed. Keep the unit in its original packaging attitude, lock the drum so it cannot rotate freely, and if it must be dismantled, place it upright or in the maker's specified attitude — never drag or roll it. Fit protective sleeves on journals and bearing seats and coat them with anti-rust grease.

Extraction columns. Column internals are mostly thin-walled and easily deformed or displaced. Fit temporary support rings between column sections to preserve roundness, pack packing material separately and keep it dry, and store pulse generator diaphragms and valves away from light and compression as rubber parts.

A point common to both: every dismantling operation should leave assembly marks inside the case. Once the balancing orientation of a centrifugal extractor or the tray direction of a column is installed incorrectly, commissioning time multiplies.

Pumps, Valves and Flow Control Parts

Pumps and valves on a rare earth separation line work in hydrochloric, sulfuric or nitric media, often with organic phase and suspended solids, so materials lean toward linings and corrosion-resistant alloys. Shippable parts include centrifugal pump casings and impellers, magnetic drive pump containment shells and inner rotors, metering pump heads, diaphragm valve bodies and diaphragms, fluoropolymer-lined ball and butterfly valves, and flow meter tubes and electrodes.

The magnetic drive containment shell is a badly underrated wear part: it is thin-walled and low in stiffness, and once crushed into a dent the magnetic coupling gap changes, efficiency collapses and the pump can fail. Have an internal support former made and fix the shell in its own EVA cavity. Lined parts should never be stacked in layers, because sustained compression separates the lining from the metal substrate. The general logic for pump and valve protection is set out in Pump and Valve Parts Cases, while shell selection for lined and corrosive service is covered in Corrosion Resistant Enclosures.

Materials and Corrosion Control in Acidic Organic Media

Two things make the rare earth separation medium unusual: acidity swings widely, from weak acid in extraction to strong acid in stripping; and organic and aqueous phases coexist, producing combined aqueous-organic corrosion and swelling.

On the metal side, the main modes are chloride pitting and stress corrosion cracking in hydrochloric systems, uniform and crevice corrosion in sulfuric systems, breakdown of the passive film by fluoride complexes, and localized low-pH attack caused by acidic traces in the organic phase. For material selection, 316L works in dilute hydrochloric acid but has limits in high-chloride service, duplex 2205 and 904L resist chloride better, titanium suits oxidizing media, and fluoropolymer or rubber lining controls cost in mainstream designs.

On the non-metal side, swelling is equally serious. P507, P204 and Cyanex type extractants with kerosene or sulfonated kerosene diluents swell some rubbers, especially NBR, by more than ten percent in volume, which destroys seals and blisters linings.

A sensible cleaning sequence is drain the organic phase first, neutralize the aqueous phase second, rinse and dry last. Draining the organic phase first keeps solvent out of later process steps; a weak or dilute alkali neutralizes residual acid; deionized water rinsing with conductivity checks confirms the result; and the part is blown dry before closure. Extractant compatibility and environmental disposal must follow the specific grade and local regulations. The parameters here are engineering practice references; the equipment maker's technical file and the site quality plan take precedence.

Compliance and Protection for Radioactive Associated Materials

Rare earth ores often carry associated natural radionuclides such as thorium and uranium, which can concentrate locally in the extraction and enrichment stages. Packaging for rare earth separation equipment is therefore not merely industrial packaging; it can also touch the transport rules for radioactive material.

Three situations must be distinguished: surface contamination left on equipment, separately existing radioactive liquid or residue, and equipment that has been adequately decontaminated. The management path differs for each. Once decontamination meets limits, surface contamination is below the specified level and a test report is issued, the equipment can be shipped as ordinary industrial goods. If decontamination is incomplete, it falls under radioactive material transport rules, involving package category, surface dose rate, transport index, marking and declaration.

Classification, package category and documentation must be confirmed against the applicable regulations and the carrier's requirements; this article does not replace the regulatory text or the competent authority's interpretation. For parts with a radioactive risk, keep records at the decontamination, survey and packaging stages separately, and choose a case whose liner can be replaced as a whole so that the case itself does not have to be scrapped after contamination.

Case Shell Materials and Structural Design

The corrosive and radioactive risks of rare earth separation parts impose a dual requirement on the shell: chemical resistance plus ease of decontamination.

Structural design points. Avoid dead corners and threaded holes in the cavity; use generous radii and removable liners so that flushing and decontamination can be verified. Form a sump and drain at the base so leaked liquid cannot pool. Add side reinforcement ribs to raise bending stiffness. On heavy cases, provide forklift pockets and mark the centre of gravity. Where radioactive contamination is possible, the liner should be removable as a whole, and the shell surface finished smooth to make decontamination easier.

Material compatibility must be checked item by item: the compatibility of shell plastics with extractants and diluents must be verified, because some solvents soften PE and PP or cause stress cracking. The compatibility approach in Corrosion Resistant Enclosures is a useful reference. If organic vapour may persist inside the case, choose a higher solvent-resistance grade or add a barrier liner bag.

Sealing Classes: IP65 / IP67 with IEC 60529 and GB/T 4208

Dust and water ingress protection is classified under IEC 60529 or the equivalent GB/T 4208, written as IP followed by two digits: the first covers solids (0–6), the second liquids (0–9K).

In rare earth service the IP class carries an extra meaning: it must not only keep external water out, it must also keep internal contamination in. A case holding radioactive or strongly corrosive parts should therefore be verified for two-way sealing — confirming that external water cannot enter and that internal liquid cannot seep out. Use a primary seal plus a secondary seal, design the O-ring groove for 15–25% compression, and hold contact surfaces to Ra 1.6–3.2 μm. Frequently opened cases should carry one gasket along the hinge side and one along the latch side, with corners moulded as a single piece to reduce joints.

Seal materials must match the medium: EPDM resists acid and weather but has limited oil resistance, FKM resists solvents better, and PTFE encapsulation suits strong corrosive contact faces. When choosing between IP54, IP65 and IP67, see IP65 vs IP66 vs IP67 Differences.

Cushioning and Compartmentalized Liner Options

The liner has to locate, cushion and isolate, and it must be compatible with the medium. That last point matters more in rare earth service than in ordinary industrial packaging, because a foam swollen by extractant loses cushioning fast and can contaminate the part.

Three compartment routes are common. Removable dividers suit large batches of similarly shaped pump and valve parts and adapt to each batch by repositioning. CNC-machined EVA cavities follow the 3D contour for high locating accuracy, ideal for drum accessories, probes and valve plugs. XPE or IXPE thermoformed liners are seamless and moisture resistant, suited to wrapping medium and long parts and plates.

For parts that may contact organic phase, add a PTFE or PVDF isolation film between liner and part: it blocks the solvent and is easy to replace. Aim for a coverage ratio of 60–75% for precision brittle items and 40–60% for heavy rigid bodies, and fill awkward recesses with shaped blocks so nothing hangs unsupported. Resilience and compression set data across foams are in Foam Material Comparison, and the trade-off against removable dividers is discussed in Divider versus Foam.

Latches, Hinges, Pressure Equalization Valves and Stacking Load

The moving parts of a case decide whether protection holds for the whole journey.

Latches. Use self-locking, vibration-resistant catches, four to eight per case, evenly loaded. Where compliance marking is involved, add a lock hole or seal position so that handover can be confirmed. Hinges. Stainless pins in engineering-plastic bodies avoid galvanic corrosion, and long cases need three or more hinges to spread torque. Pressure equalization valves. Day-night temperature swings and altitude changes in transit create a pressure differential that can bulge the shell or draw the gasket into its groove. A valve with an ePTFE hydrophobic membrane equalizes pressure while blocking liquid water and dust. Check airflow rate, cracking pressure and the match with the declared IP class, and inspect the membrane for clogging by scale fragments or dust.

Stacking load must be checked against warehouse and container layer counts.

Stack so the upper case bears on the side walls and corner posts rather than directly on the lid, and rotate stock during long storage so that sustained static load does not creep the shell. For cases carrying radioactive marking, stacking and storage should also follow zone management and keep the marking visible, rather than mixing them with other materials.

Temperature, Humidity, Salt Spray and Transport Testing

A packaging plan has to be verified by test. Rare earth separation parts often travel by sea and face high humidity, salt and wide temperature swings.

Three quick field checks: confirm visually that the liner is compressed with no void at contact faces; check gasket contact for creases or breaks at corners; and after closing, run a simple airtightness or pressure-decay check to confirm there is no leak path.

Salt spray duration depends on the local environment, transit time and maintenance interval, so the ranges above are engineering references and are not a service-life warranty. ISTA and ASTM test levels must likewise be selected for the actual route, and passing a test does not promise zero damage under any specific logistics condition. For test design, see GB/T 4857 Transport Packaging Cases and ISTA Transport Testing Procedure.

Customization, OEM/ODM and Acceptance Criteria

Rare earth separation parts are mostly non-standard, and an off-the-shelf case rarely fits. A sensible sequence runs: requirement confirmation (part list, dimensions, weight, medium residue and transport route), 3D survey and design, liner prototype and trial fit, tooling and first-article approval, small-batch validation, then volume production. JUNZHIJIA offers machined liners, case tooling, logo printing and documentation packages, supports OEM and ODM models, and can supply material certificates, test reports and packing lists on request.

Acceptance criteria should be quantified rather than left to a vague visual pass.

The programme is delivered alongside Kexin New Materials (Guangdong) Co., Ltd.

Frequently Asked Questions FAQ

Q: What happens if mixer-settler parts are packed while still wet with organic phase?

A: The most direct result is swelling damage to the liner and seals, followed by case contamination from leaking residue. P507 and P204 extractants with kerosene-type diluents swell or soften NBR rubbers and some PE and PP foams, with volume changes of more than ten percent, which lifts the liner, distorts the gasket groove and drops the protection class quickly. If residue seeps out in transit it contaminates the case, the pallet and even neighbouring goods, leaving solvent marks that are hard to clean. The correct order is to drain and recover the organic phase, neutralize residual acid with a weak alkali, rinse with deionized water while checking conductivity, and dry before closing. If a part cannot be cleaned immediately, seal it on site in a barrier inner bag and record the residue condition. Add a PTFE or PVDF isolation film between liner and part so the solvent is blocked and the film can be replaced.

Q: What rules must be followed when transporting a centrifugal extractor drum?

A: Preserve balancing accuracy and geometric roundness. The drum runs at high speed, so any impact, slight distortion or journal scratch is amplified into vibration that affects separation efficiency and bearing life. Keep the unit in its original packaging attitude, lock the drum so it cannot rotate freely, and if it must be dismantled, place it in the maker's specified attitude, never dragging or rolling it. Fit protective sleeves on journals and bearing seats and coat them with anti-rust grease. Drain and dry the drum interior so that residual liquid cannot shift and create imbalance in transit. Include assembly marks in the case that state the balancing orientation and the reassembly order, because an incorrect installation multiplies commissioning time. Pack the inlet and outlet piping and seals in separate compartments so they never touch the drum metalwork, and re-check runout and appearance after transport as an acceptance record. Confirm the drum rotation lock and log the lock torque in the handover file, because a drum that turns in transit can rub its seals flat.

Q: Why does a magnetic drive containment shell need special protection?

A: Because it is a thin-walled shell with low stiffness, it dents or cracks easily under load, and its shape accuracy directly sets the magnetic coupling gap and the torque it can transmit. If it ships in the same compartment as the pump body or impeller, compression and vibration produce deformations that are hard to see, and the installed result is reduced flow, abnormal temperature rise or outright loss of coupling. The correct practice is to have an internal support former made, fix the shell in its own CNC-machined EVA cavity with no free travel, keep it away from heavy metal parts, and pack it separately if necessary. After opening, check roundness with a template or plug gauge before assembly. Protection logic for similar thin-walled parts follows pump and valve practice, as described in Pump and Valve Parts Cases, and if the shell material is sensitive to organic phase or acid, add an isolation film and verify compatibility. Keep the packing record with the pump so the same treatment is repeated when the part returns as a core.

Q: What extra precautions apply when rare earth equipment carries trace radioactivity?

A: First determine the classification, then choose the packaging path. Equipment carrying residues of natural radionuclides such as thorium and uranium must first be surveyed for surface contamination and dose rate, with a report issued. If decontamination meets limits and surface contamination is below the specified level, it ships as ordinary industrial goods; if decontamination is incomplete, it falls under radioactive material transport rules covering package category, transport index, marking and declaration. In engineering terms, add a leak-proof inner bag, keep the outer case sealed and structurally sound so that rain cannot wash contamination outward, apply dangerous goods and radioactive labels plus orientation marks per the applicable regulations, carry the survey report, declaration and emergency response card, and issue gloves, face shields and dosimeters for opening and lifting. Classification and documentation requirements must be confirmed with the applicable regulations and the carrier, and this guidance does not replace the regulatory text. Keep one decontamination log per case so a later inspection can see what was done and when.

Q: Do extractants and diluents attack the case itself, and how should material be chosen?

A: Yes, especially with long contact or vapour accumulation. Some solvents soften PE and PP, cause stress cracking or swell them, and they also take the resilience out of ordinary foams. Selection starts with a complete medium list and an item-by-item compatibility check, rather than a single acid and alkali resistance claim. In practice, choose a higher solvent-resistance grade for the shell, or fit a replaceable barrier liner bag and a PTFE or PVDF isolation film inside the cavity so the solvent never touches the shell itself. Avoid EPE for liners because it swells in strong solvents, and prefer denser EVA or closed-cell IXPE. Choose seals between EPDM and FKM according to the specific solvent, with FKM usually the better solvent barrier, and control storage temperature and keep cases out of direct sunlight, because heat accelerates both swelling and ageing. Final compatibility data must come from the material supplier's chemical resistance table and from measured results.

Q: How should a rare earth separation plant choose between IP65 and IP67 cases?

A: Weigh two directions at once: external water must not enter, and internal contamination must not escape. Covered in-plant shuttles are served by IP54 splash protection; open yards or rain-exposed transfer need IP65; sea freight, rainy regions or possible brief immersion call for IP67. Note that IP67 defines 30 minutes of immersion at one metre, not continuous submersion. Where corrosive or radioactive residue is possible, add a two-way seal verification that confirms both that water cannot enter and that liquid cannot seep out. Another overlooked factor is gasket ageing: ultraviolet light, ozone and temperature cycling harden rubber and increase compression set, so the effective rating drops over time and gaskets need scheduled inspection and replacement. Frequently opened cases should carry one gasket along the hinge side and one along the latch side, corners moulded as a single piece, to reduce joint leak paths and keep the verified class intact. Where a case is opened repeatedly, consider a stainless frame version so the structure itself can be washed down.

Q: What milestones should be confirmed when customizing cases for non-standard extraction equipment?

A: Five checkpoints are recommended. First, requirement confirmation: provide the part list, 3D models or measured dimensions, individual weights, centre of gravity and transport route, and state the residue type and any radioactive risk. Second, design: settle the shell process, whether rotational moulding, injection moulding or frame, plus liner material and compartment layout, and issue structural and sealing drawings. Third, prototype and trial fit: build the liner prototype first and verify fit, handling convenience and solvent compatibility. Fourth, tooling and first-article approval: check dimensional tolerance, two-way seal verification and load test results. Fifth, volume production only after small-batch validation. Agree in advance on the documentation package — material certificates, test reports, packing list and location drawing — and on marking and logo printing for OEM and ODM. Keep the drawings and the first-article report in one file per part number, so a later order reuses the approved design instead of starting the review again from the beginning, and record the approval date for traceability.

Q: Which transport tests should rare earth separation part packaging pass, and when is it good enough?

A: Combine tests according to the route rather than relying on a single item. A sea-dominated route typically combines neutral salt spray per GB/T 10125 for metal and hardware corrosion, vibration per the GB/T 4857 series or ASTM D4169 for cushioning and fastening, static stacking for long-term compression, and temperature-humidity cycling for condensation. For parts that may leak, add a two-way pressure decay verification, and where handling is rough add ISTA 1A, 2A or 3A drop and impact. Define pass criteria in advance: no part deformation or scratches, no liner collapse or swelling traces, the sealing class re-tested and passed, and no broken or loose hardware. Be clear that salt spray duration and test levels depend on the local environment and transit time, so a pass represents that set of conditions only. It is not a service-life warranty.

Conclusion and Related Reading

Rare earth separation packaging translates three residues, a radioactivity risk and precision surfaces into shell structure, liner layout and decontamination procedure. Drain, neutralize, then verify: the order cannot be reversed.

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