Hangbo Alloy Group
Shanghai · Est. 2012
Heap leach, SX-EW and solvent extraction expose plant equipment to hot acid, chloride and H2S. See which nickel alloys resist pregnant leach solutions.
Hydrometallurgy now produces the majority of the world's copper, nickel, cobalt and uranium, and it is the fastest-growing route for critical-metal recovery. At its heart are corrosive, abrasive circuits - heap and tank leach, solvent extraction (SX) and electrowinning (EW) - where pregnant leach solution (PLS) carries sulfuric or hydrochloric acid, dissolved chloride, and often hydrogen sulfide. Carbon steel and even duplex stainless fail quickly here, so leach plants increasingly specify nickel alloys for the components that cannot be allowed to corrode through.
In a typical heap-leach operation, dilute sulfuric acid is sprinkled over an ore stack; the resulting PLS is collected, clarified and pumped to SX, where an organic solvent pulls the target metal out before electrowinning plates it onto cathodes. Every stage is warm, acidic and laden with solids and entrained gas. Conventional carbon steel leach tanks are lined, but agitators, pumps, piping, launders and SX mixer-settler hardware see thin-film and crevice conditions where liners cannot reach.
The corrosion driver is not just acid concentration but the anion mix: chloride from the ore or from HCl leach accelerates pitting and crevice attack, while dissolved H2S can appear in solution and in the vapor space above it. Grade selection therefore has to satisfy both a sulfuric acid resistance requirement and a chloride/sour-environment requirement at once.
PLS chemistry varies with ore body, but several features recur. Sulfate is almost always present at high concentration; chloride ranges from trace to several percent in brine-leach and some laterite processes; and biologically or chemically generated H2S can appear in solution and in the vapor space above it. Where chloride exceeds a few thousand ppm, standard austenitic stainless begins to pit, and the risk of chloride stress-corrosion cracking in welded or cold-formed parts becomes real.
For sour zones, the alloy must also meet sulfide-stress limits analogous to those in our NACE MR0175 sour-service note. High-molybdenum nickel alloys resist both the chloride pitting and the H2S environment, which is why they are specified for the most critical leach and SX hardware rather than merely as a cost option.
For mildly acidic, low-chloride PLS, a high-alloy austenitic such as Alloy 28 offers good sulfate resistance at lower cost, as covered in our Alloy 28 chemical-processing reference. As chloride and oxidizing conditions rise, the Hastelloy C-family becomes the default: C-276 for general leach and SX duty, and C-22 where the safety margin against pitting must be larger.
The trade-off between the two is quantified in our C-276 vs C-22 comparison. Electrowinning cells and acid-mist exposure add an oxidizing, aerated dimension that favors the higher-chromium C-22 or Alloy 59. The practical rule is to size the alloy to the worst week of operation, not the average assay, because leach chemistry spikes with weather and ore changes.
Two failure modes dominate leach-plant outages: crevice/pitting corrosion under deposits and chloride stress-corrosion cracking at welds and bends. Mitigation starts with alloy choice (higher molybdenum = higher PREN, the pitting-resistance metric explained in our PREN guide), continues with good fabrication - no sharp bends, full-penetration welds, and avoidance of galvanic couples to carbon steel - and ends with inspection of crevices where solids settle.
Where the circuit is genuinely sour, confirming compliance with MR0175 and pairing the alloy with conservative stress design prevents the sudden crack failures that lining alone cannot stop. Hangbo supplies the qualified grades in the product forms a leach plant needs, with certificates that let the plant's corrosion engineer close out the materials specification.
Low-chloride PLS is well handled by Alloy 28, while chloride-bearing or more oxidizing leach liquors need the Hastelloy C-family; our Alloy 28 reference and C-276 vs C-22 comparison show where each is appropriate.
High-molybdenum nickel alloys resist the combined chloride-plus-sulfide environment of sour leach zones and meet limits comparable to those in our NACE MR0175 note. Carbon steel and many stainless grades do not, and crack or corrode rapidly.
C-276 covers most leach and SX duty; C-22 adds margin against pitting and crevice attack where chloride and oxidizing conditions are higher, notably in electrowinning acid mist. The trade-off is detailed in our comparison guide.
We supply plate, sheet, pipe, fittings and fabricated weldments in the qualified grades, supported by the chloride-cracking guidance in our SCC article and EN 10204 3.1 certification for plant materials specifications.
As a dedicated nickel alloy manufacturer serving chemical processing sectors, Hangbo Alloy Group supplies the grades discussed here across all standard product forms — including plates & sheets, seamless tubes & pipes, and forgings — with full ASTM/ASME documentation and EN 10204 3.1 certification. Our material is specified for applications where corrosion resistance, high-temperature strength, and traceable quality are non-negotiable. See our production & testing facilities for more on how every heat is verified.