Lined Pipe for Mining and Metals

Hydrometallurgy is corrosion on purpose. Sulfuric acid dissolves copper and uranium out of ore, cyanide dissolves gold, chlorine and hydrochloric acid dissolve platinum-group metals and rare earths, and every one of those solutions then has to be pumped, often with solids in it, over long outdoor runs. Marspec Technical Products fabricates the PTFE-, PVDF- and polypropylene-lined pipe spools and supplies the lined fittings, valves and accessories built for leach solution, electrolyte, reagent and acid-plant service, shipped from Fairhope, Alabama. Call 251-625-4949 with a flow sheet and line list.

After more than half a century in plastic-lined piping we know the circuits. Contact us online with the solution chemistry, the solids content and the temperature and we will recommend a liner.

Hydrometallurgy, circuit by circuit

Copper: leach, solvent extraction and electrowinning

Heap and stockpile leaching drips a raffinate of 5 to 20 grams per liter sulfuric acid over crushed ore and collects a pregnant leach solution carrying a few grams per liter of copper. Solvent extraction loads that copper onto a hydroxyoxime extractant in a kerosene diluent, strips it with spent electrolyte at roughly 160 to 200 grams per liter sulfuric acid, and electrowinning plates it out of that electrolyte at 110 to 120 F. Raffinate and PLS at ambient run in PTFE-lined pipe, with polypropylene available where a specification calls for it; the loaded organic and the mixer-settler interconnects go in PVDF or PTFE because the diluent swells polypropylene over time; and the warm electrolyte and bleed streams run in PVDF or PTFE. Lined strainers catch the crud that forms at the organic interface before it reaches the electrolyte pumps.

Gold and silver: cyanide, carbon and acid wash

Oxide ore is heap-leached with dilute sodium cyanide at a pH of 10 to 11, held there with lime; sulfide ore is roasted or pressure-oxidized in an acidic autoclave, neutralized with limestone, then cyanided in carbon-in-leach or carbon-in-pulp tanks. Loaded carbon is acid-washed with about 3 percent hydrochloric acid to remove calcium scale, then eluted with hot caustic and cyanide, near 280 F under pressure in a Zadra circuit, and the gold is electrowon and smelted. Spent solution is detoxified with sulfur dioxide and air, hydrogen peroxide or Caro's acid. Cyanide reagent, barren solution, the acid wash and the hot pressure strip are all PTFE service, with polypropylene available for the cyanide and barren lines where specified, and the cooled autoclave discharge, acidic and loaded with ferric sulfate and solids, is PVDF-lined with lined diaphragm valves.

Smelters, refineries and specialty metals

A copper smelter's acid plant scrubs the furnace gas with weak acid that carries fluoride, chloride and arsenic, among the most corrosive streams in metallurgy, before converting the sulfur dioxide to 93 to 98 percent sulfuric acid. The weak acid loop is PTFE; the product acid stays in carbon steel at low velocity and enters lined pipe wherever it is diluted. Electrorefining runs copper sulfate electrolyte with an acid bleed, and slimes leaching for selenium, tellurium and precious metals uses hydrochloric acid and chlorine. Platinum-group metal refineries leach matte in sulfuric acid and dissolve the concentrate in hydrochloric acid and chlorine, uranium and beryllium mills leach in sulfuric acid, rare earth plants separate in hydrochloric acid extraction trains, and magnesium plants electrolyze chloride brine into metal and chlorine. Wet chlorine, hot chloride brines and mixed acids are the services fluoropolymer liners were developed for, replacing titanium, nickel alloys and tantalum.

Liner choice in a mill

• Raffinate, PLS, barren cyanide solution and lime slurry at ambient: PTFE, with polypropylene where specified
• Loaded organic, electrolyte and acid bleed streams: PVDF or PTFE
• Gas-cleaning weak acid, HCl acid wash and chlorine leach liquor: PTFE in vented housings
• Autoclave discharge, acidified tailings and thickener underflow: PVDF
• Pressure strip, hot caustic and any acid above 275 F: PTFE
• Hydrogen peroxide and Caro's acid: PVDF or PTFE, vented

Valves, slurry and the spool package

Lined plug and diaphragm valves are the mill standard where solids are present, because neither depends on a seat that grit can score. PFA-lined ball valves give tight shutoff on reagent lines, lined butterfly valves cover the large raffinate and PLS headers, lined check valves protect dosing pumps and lined sampling valves draw assay samples. Patterns are on our lined valves page, and we mount and test actuators and positioners in-house for automated packages.

A mine package from us is usually 2" through 12" lined carbon steel spools built to isometrics in lengths up to 20 ft with class 150 ANSI B16.5 rotating flanges, lined fittings to match, PTFE-bellows expansion joints for long outdoor racks, PTFE spacers and spectacle blinds at the tankhouse battery limits, lined Y and basket strainers, and sight glasses on the reagent lines. Abrasion is the mining-specific question: PVDF is the strongest of the three liners and takes slurry best, and we size the liner to solids content and velocity. The size and liner range is on our lined pipe and fittings page; strainers, blinds and expansion joints are under piping accessories.

Sun, altitude and winter matter. A rack in the Arizona or Nevada sun runs well above ambient and polypropylene loses pressure rating as it warms, so hot outdoor acid lines are PVDF or PTFE. The same districts sit at elevation, where 50 percent caustic crystallizes near 54 F, dilute acid freezes, and electric tracing or clamp-on steam heaters with heat-transfer compound from our temperature maintenance line keep them moving inside the liner's rating. Vacuum ratings by liner and size, for filter feed and vacuum receivers, are on our technical details page.

Mining country, standards and ordering

Arizona's porphyry copper belt from Morenci to Bagdad holds the largest concentration of leach and SX/EW plants in the country. Nevada's Carlin and Cortez trends produce most of the nation's gold, and its lithium projects are in Humboldt County and Clayton Valley. Utah pairs the Bingham Canyon smelter and its acid plant with the Great Salt Lake magnesium and potash works and uranium and beryllium mills. Montana has the Butte copper concentrator and the country's only platinum and palladium mines and refinery at Columbus. Minnesota's Iron Range ships most of the nation's iron ore, and Idaho's Silver Valley and phosphate districts round out the map. The battery and lithium plants and steel pickling lines downstream run on the same liners.

Our lined products comply with ASTM F1545, fittings conform dimensionally to ANSI B16.5 and are welded to ASME B31.3 by welders certified to ASME Section IX, and every lined part is spark tested at a minimum of 10,000 volts. Call 251-625-4949 with isometrics or a line list, or contact us online. We ship nationwide and fabricate custom spools in our own shop.

FAQ: Lined Pipe for Mining and Metals

Which liner holds up on raffinate and pregnant leach solution over long outdoor runs?

PTFE: it is unaffected by sulfuric acid at leach strength and keeps its pressure rating where the rack sits in full sun or the solution is warm. PVDF is an alternative for the warm runs, polypropylene is available for ambient runs where a specification calls for it, and we add lined expansion joints for the thermal growth.

Can lined pipe handle the hot caustic and cyanide pressure strip on our carbon circuit?

Yes, in PTFE. A Zadra strip runs near 280 F under pressure, above the limits of PVDF and polypropylene, and PTFE is rated to 450 F and is unaffected by caustic and cyanide. The hydrochloric acid wash ahead of it is PTFE as well, in a vented housing.

What do you recommend for the weak acid from a smelter gas-cleaning plant?

PTFE. The weak acid carries fluoride, chloride and arsenic, which attack stainless, nickel alloys and glass alike. PTFE-lined spools with PTFE-lined plug valves are the standard, and the fluoride is the reason glass-lined equipment is not an option.

How much solids can a lined pipe carry?

Slurry is a velocity and particle question more than a chemistry question. PVDF takes abrasion best, we keep velocities moderate and avoid sharp changes of direction, and lined plug and diaphragm valves tolerate grit. Send us the solids content, particle size and velocity and we will tell you where lined pipe fits and where it does not.