Application Area

In high-pressure acid leaching (HPAL) processes—whether for gold or nickel-cobalt ores—the operating environment for diaphragm pump check valves is far more severe than in conventional slurry pumping. For gold smelting, high-temperature, high-pressure oxidation pretreatment (e.g., pressure oxidation) is often employed, while HPAL of nickel-cobalt laterite ores uses concentrated sulfuric acid at temperatures of 200–220 ℃and pressures up to 5 MPa. Such high-temperature, strongly acidic media impose extremely high demands on the corrosion resistance of valve materials. Standard stainless steels or conventional rubber seals would fail within hours. Therefore, the sealing components of the valve must be made from specially developed elastomer (e.g. Viton or special EPDM), while metallic parts require corrosion and wear resistant alloys, including duplex stainless steel, Stellite etc.

Left: Premature API-5 valves after changed out in gold HPAL            Right: Tasou all-forged API-5 valve for gold HPAL

An additional challenge is the presence of high-hardness solid particles in the hot slurry—for example, quartz and pyrite in gold ores, or chromite and hematite in nickel-cobalt ores. These particles, flowing at high velocity, cause severe abrasive wear on the conical valve and seat surfaces. Even an alloy with excellent corrosion resistance will rapidly suffer erosion, scoring, or spalling if its hardness or toughness is insufficient. Consequently, the selected alloy must strike a balance between corrosion resistance and wear resistance. This is often achieved by cladding wear resistant alloy on corrosion resistant matrix or using high-chromium white cast irons, combined with precisely controlled heat treatment (quenching and tempering) to obtain a high-hardness martensitic matrix or a precipitation-hardened microstructure. Such requirements place stringent demands on alloy processing, including melting, casting, forging, and post-treatment heat treatment.

All-Metal API-12 valve in valve housing                                                                                 Drop legs of autoclave pumps

Among all the applications we have encountered to date, nickel-cobalt smelting under HPAL conditions is the most severe. Because the operating temperature often exceeds the service limit of most elastomers, the check valve must adopt an all-metal design. The key to extending service life is selecting a metallic material that combines excellent wear resistance, corrosion resistance, and good fracture toughness. Therefore, their chemical composition design, melt protection during processing, and heat treatment windows are extremely narrow—this represents the core manufacturing challenge for diaphragm pump check valves in such aggressive service.