{"id":7876,"date":"2026-11-10T00:40:59","date_gmt":"2026-11-10T08:40:59","guid":{"rendered":"https:\/\/changyupump.com\/?p=7876"},"modified":"2026-11-13T01:06:52","modified_gmt":"2026-11-13T09:06:52","slug":"metallurgy-slurry-pump-smelter-slag-scale-oxide","status":"publish","type":"post","link":"https:\/\/changyupump.com\/id\/blog\/metallurgy-slurry-pump-smelter-slag-scale-oxide\/","title":{"rendered":"Metallurgy Slurry Pumps: Selection for Smelter Slag, Scale and Metal Oxide Slurry"},"content":{"rendered":"\n

Quick answer:<\/strong> A metallurgy slurry pump handles hot, abrasive, mildly acidic smelter streams.<\/strong> Four variables decide the specification. Slurry temperature: elastomer linings stop at roughly 80 \u00b0C. Particle shape: granulated slag fractures into glassy shards that cut rather than round off. Solids specific gravity: metal oxide slurries run 4.2\u20135.2 and settle within seconds. And pH, which swings between campaigns. High-chrome white iron covers most slag duty, UHMWPE and PFA cover the acid side, duplex stainless sits between them.<\/p>\n\n\n\n

Most catalogues treat “metallurgy” as one application. A smelter asks four different things of a metallurgy slurry pump, sometimes within fifty metres of pipe. We have supplied into copper, lead, zinc, nickel and ferroalloy plants, and the failures we get called in to fix are rarely hydraulic. They are material choices made on the wrong assumption \u2014 a rubber-lined unit specified from a mill-duty datasheet, a cast iron volute asked to survive a launder flush.<\/p>\n\n\n\n

Typical smelter duty ranges<\/h3>\n\n\n\n
Parameter<\/th>Typical range<\/th>Why it matters<\/th><\/tr><\/thead>
Slurry temperature<\/td>40\u201395 \u00b0C; granulation 75\u201395 \u00b0C<\/td>Sets the lining ceiling \u2014 above 80 \u00b0C elastomers are out<\/td><\/tr>
Solids by weight<\/td>5\u201350 %; slag granulation 10\u201330 %<\/td>Drives wear rate and settling velocity<\/td><\/tr>
Particle size<\/td>d50 0.05\u20138 mm; cleanout lumps to 100 mm<\/td>Decides impeller passage and impact tolerance<\/td><\/tr>
Solids SG<\/td>2.6\u20133.2 slag; 4.2\u20135.2 iron and metal oxide<\/td>Head and power must be corrected for SG<\/td><\/tr>
pH<\/td>2\u201310, frequently swinging<\/td>Rules high chrome in or out of acid duty<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
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What Makes Smelting Duty Different From Leaching Duty<\/h2>\n\n\n\n

A hydrometallurgy circuit has one enemy: acid. A smelter has three, arriving together.<\/p>\n\n\n\n

The particles cut.<\/strong> Granulated slag quenches into glass and fractures with conchoidal breakage \u2014 thin, sharp, hard shards. Silica-rich ferrous slag sits around 6\u20137 on the Mohs scale; fayalite copper slag is similar. Rounded tailings deform a surface; these shards slice it. Rubber resists indentation and rebound far better than a sharp edge dragged across it at 3 m\/s, which is why a lining that gives three years in a tailings line can be cut through in a slag launder. Composition shifts with furnace and campaign, so Euroslag<\/a> publishes chemistry ranges rather than a single slag specification \u2014 worth checking before you treat one plant’s experience as another’s.<\/p>\n\n\n\n

The slurry is hot.<\/strong> Granulation water recirculates through cooling towers and returns to the granulation box, so the pump normally sees 60\u201395 \u00b0C, not ambient. Rubber’s ceiling is about 80 \u00b0C; above that it takes compression set and the lining-to-casing bond becomes the weak point.<\/p>\n\n\n\n

The chemistry drifts.<\/strong> Granulation water runs near neutral, but acid plant weak acid, scrubber blowdown and converter hood wash can drop to pH 2\u20134 during an upset. Any material relying on a passive oxide film will pit in a weekend of that.<\/p>\n\n\n\n

Then add density. Slag slurry runs 1.3\u20131.6 SG; metal oxide slurry runs higher, because the solids themselves are heavy. This is where sizing most often goes wrong \u2014 pump chosen from a water curve, motor chosen from the water power, and the first hot weekend tells the story.<\/p>\n\n\n\n

Four Streams, Four Different Pumps<\/h2>\n\n\n\n

1. Furnace slag and granulation slurry<\/h3>\n\n\n\n

Slag tapped at 1,450\u20131,700 \u00b0C is quenched, screened, and the fines report to a settling sump. The metallurgy slurry pump on this stream moves 10\u201330 % solids at 75\u201395 \u00b0C with d50 in the millimetre range. Wear is cutting erosion at the volute throat and impeller discharge, plus impact at the suction eye from a lump that got past the screen.<\/p>\n\n\n\n

This is high-chrome territory \u2014 hypereutectic white iron in the Cr26\u2013Cr28 range at 58\u201363 HRC<\/strong>, with 25\u201340 mm of section at the throat so wear allowance is designed in rather than discovered. We set the impeller passage wide relative to the duty point; a slight efficiency sacrifice buys far fewer blockages.<\/p>\n\n\n\n

2. Skull, scale and launder cleanout<\/h3>\n\n\n\n

Every smelter has a stream nobody puts on the P&ID: the washdown. Launders get flushed, ladles cleaned, scale pits dug out, and the slurry carries lumps to 100 mm plus tramp steel. Impact wear, not abrasion, is the failure mode<\/strong> \u2014 and a blockage costs more than a liner. Here we argue for a vertical sump pump with an oversized suction, or a horizontal unit with a large-passage semi-open impeller and clean water flush at the gland.<\/p>\n\n\n\n

3. Converter and hood dust slurry<\/h3>\n\n\n\n

Converter off-gas washing produces a fine slurry (d90 usually under 150 \u00b5m) that is acidic from SO\u2082 and SO\u2083 absorption \u2014 pH 2\u20135 is common. The failure mode flips: this is corrosion-erosion, not abrasion<\/strong>. Fine acidic solids polish away corrosion product and expose fresh metal, so a static coupon test is optimistic by a factor of two or three.<\/p>\n\n\n\n

Duplex stainless (2205\/2507) or a PFA-lined casing is the usual answer, provided the PFA is anchored properly. Our CYG series uses a moulded 8\u201320 mm PFA lining sintered into a steel body, which avoids the cracking that plagues loosely bonded liners.<\/p>\n\n\n\n

4. Metal oxide slurry<\/h3>\n\n\n\n

Iron oxide dust, TiO\u2082 calciner slurry, zinc fume wash, mill scale: fine, dense, fast-settling. Iron oxide runs about 5.2 SG, TiO\u2082 about 4.2. A 30 % by weight iron oxide slurry has an approximate SG of 1.32<\/strong>, assuming iron oxide SG 5.2 and water SG 1.0, and settles several times faster than silica at the same concentration.<\/p>\n\n\n\n

Two consequences. Size on real SG, not 1.0 \u2014 a 45 m duty at SG 1.9 draws almost twice the water power. And keep line velocity above carrying velocity, typically 1.8\u20132.5 m\/s, or you build a plug in the horizontal run and then cook the pump clearing it.<\/p>\n\n\n\n

Material Selection for Metallurgy Slurry Pumps<\/h2>\n\n\n\n
Material<\/th>Hardness<\/th>Temp ceiling<\/th>Best for<\/th>Weak against<\/th><\/tr><\/thead>
High-chrome white iron (Cr26\u201328)<\/td>58\u201363 HRC<\/td>200 \u00b0C+<\/td>Slag, scale, coarse angular solids<\/td>pH below 4 without alloy upgrade<\/td><\/tr>
Natural rubber lining<\/td>40\u201355 Shore A<\/td>~80 \u00b0C<\/td>Fine rounded solids, acid slurry<\/td>Sharp shards, large lumps, hot duty<\/td><\/tr>
UHMWPE, steel-backed<\/td>~50 Shore D<\/td>~90 \u00b0C<\/td>Acid slurry, fine low-impact solids<\/td>Coarse angular particles, tramp metal<\/td><\/tr>
PFA \/ PTFE lining<\/td>\u2014<\/td>160\u2013180 \u00b0C<\/td>Hot acid, chloride, HF<\/td>Coarse abrasion; needs rigid backing<\/td><\/tr>
Duplex 2205\/2507<\/td>25\u201330 HRC<\/td>250 \u00b0C+<\/td>Acid and abrasion together<\/td>Severe cutting wear alone<\/td><\/tr>
Alumina ceramic inserts<\/td>1,200+ HV<\/td>400 \u00b0C<\/td>Low-angle erosion, fine hard solids<\/td>Impact above 1\u20132 mm particles<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

Hardness is one input, not the answer. The same silica that scores 7 on Mohs is a respiratory hazard, and OSHA’s crystalline silica rule<\/a> shapes how slag and dust handling areas are ventilated and maintained \u2014 occasionally the reason a wet transfer route is chosen over a dry one.<\/p>\n\n\n\n

The matrix is not a menu. Every row has a condition where it wins and one where it fails early, and specifying a metallurgy slurry pump means finding which condition the stream is in. We covered the mechanics, including the hardness\u2013toughness trade-off and the five wear mechanisms, in our wear-resistant slurry pump material and selection guide<\/a>.<\/p>\n\n\n\n

For smelter slag the ranking is blunt: high chrome first, ceramic inserts second (only if the screen is reliable), duplex third (only if pH forces it), elastomer last<\/strong>. For converter dust the order reverses.<\/p>\n\n\n\n

Temperature Is the Constraint Most Specifications Miss<\/h2>\n\n\n\n

We are sent more bad datasheets over temperature than any other line.<\/p>\n\n\n\n

The 80 \u00b0C figure for rubber is not a marketing number. Above roughly 80 \u00b0C, natural rubber in a slurry lining takes permanent compression set, hardness climbs, resilience falls, and the adhesive bond to the casing becomes the limiting component. A lining bonded at 20 \u00b0C will disbond at 90 \u00b0C within a few thousand hours, and the failure looks like a manufacturing defect when it is a metallurgy slurry pump specification error.<\/p>\n\n\n\n

Three rules. Ask for the temperature at the pump flange, not at the tap<\/strong> \u2014 a granulation circuit can run 95 \u00b0C at the launder and 62 \u00b0C at the pump after the cooling tower. Derate the seal with the lining: above 80 \u00b0C default to a double mechanical seal or a K-type dynamic seal with clean water. And respect thermal growth, because the coupling alignment set cold is not the alignment in service.<\/p>\n\n\n\n

Check NPSH at temperature too. Water at 90 \u00b0C has a vapour pressure near 70 kPa, which removes most of the margin on a short suction line.<\/p>\n\n\n\n

Sizing: Three Corrections That Change the Answer<\/h2>\n\n\n\n

Correct for specific gravity.<\/strong> Shaft power follows slurry density:<\/p>\n\n\n\n

P (kW) = Q (m\u00b3\/h) \u00d7 H (m) \u00d7 SG \u00f7 (367 \u00d7 \u03b7)<\/code><\/p>\n\n\n\n

A 200 m\u00b3\/h duty at 45 m, SG 1.55, efficiency 0.72, gives 200 \u00d7 45 \u00d7 1.55 \u00f7 (367 \u00d7 0.72) = 52.8 kW<\/strong>. Fit a 75 kW motor, not a 55 kW one \u2014 the next frame up is cheap next to a rewind and a lost production day.<\/p>\n\n\n\n

Do not read the water curve as the slurry curve.<\/strong> Slurries produce less head than water at the same impeller speed and flow, and the gap widens with concentration and particle size. The Hydraulic Institute standard for rotodynamic centrifugal slurry pumps<\/a> sets out the correction method.<\/p>\n\n\n\n

Keep line velocity above carrying velocity.<\/strong> For dense oxide solids, 1.8\u20132.5 m\/s horizontally; for slag granulation slurry, 2.5\u20133.5 m\/s<\/strong>. Below that the line plugs and the metallurgy slurry pump runs out on its curve until something overheats.<\/p>\n\n\n\n

Configuration Choices That Decide Maintenance Cost<\/h2>\n\n\n\n

Double casing.<\/strong> An outer pressure casing with replaceable inner liners lets the wet end be changed without breaking pipe \u2014 measured in shutdown days per year across a battery of units.<\/p>\n\n\n\n

Impeller type.<\/strong> Semi-open handles coarse solids and resists a lodged particle jamming the eye. Closed is more efficient on fine duty, but never put one on a stream carrying lumps.<\/p>\n\n\n\n

Seal arrangement.<\/strong> Packing is cheap but leaks, which is unacceptable near a hot launder. An expeller seal needs no flush water and tolerates grit, but stops working if the pump runs back. A mechanical seal is the default for hot or toxic duty, and its reliability depends on whether the flush is clean.<\/p>\n\n\n\n

Motor margin.<\/strong> 15\u201320 % above calculated shaft power<\/strong>, because oxide density varies between campaigns and slag circuits surge when a furnace is tapped.<\/p>\n\n\n\n

Which Changyu Metallurgy Slurry Pump to Start From<\/h2>\n\n\n\n

Our metallurgy and smelting pump solutions<\/a> page maps the full range to process streams. For the four duties above, these are the starting points.<\/p>\n\n\n\n

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