Severe service
From breakdown to breakthrough- Part One: Coating limitations in hydrometallurgy applications
In this two-part series, Fadila Khelfaoui and Luc Vernhes explore how valve coatings perform under the extreme conditions of hydrometallurgical processes like HPAL and POx. Part one will examine the limitations of conventional coatings and the challenges they face in severe service.
Part two will introduce VEL-8- a breakthrough ceramic coating engineered to deliver superior durability and reliability in the harshest environments.
In hydrometallurgical operations, valves are exposed to some of the most extreme service conditions in the industry. High-Pressure Acid Leaching( HPAL) and Pressure Oxidation( POx) expose equipment to elevated temperatures, high pressures, and highly corrosive slurries. These conditions strain not only valve bodies and trim but also the integrity of protective coatings, especially on sealing surfaces and moving components. Understanding the limitations of current coating technologies is essential to advancing reliability and unlocking next-generation solutions.
Understanding the process environment
HPAL and POx are both used to extract metals from ores that are difficult to treat through conventional means:
• HPAL targets nickel and cobalt recovery from laterites, operating at 250 – 300 ° C and pressures up to 65 bars, using concentrated sulfuric acid slurries.
• POx treats ores containing gold, copper, molybdenum and uranium at 200 – 230 ° C and pressures up to 40 bars, using oxygen and acid in a slurry phase.
Figure 1: Process schematic highlighting key equipment used in HPAL and POx operations.
Despite their chemical differences, both processes rely on critical equipment such as valves, pumps and autoclaves as shown in Figure 1. These components must endure highly aggressive conditions caused by hot sulfuric acid corrosion, erosion and scale buildup, particularly in feed and discharge lines. Failures in these areas are typically attributed to coating degradation rather than mechanical breakdown. As a result, coating performance is a key factor in ensuring sustained operational reliability. The global footprint of HPAL and POx plants( Figure 2) shows widespread adoption of Velan severe-service ball valves. According to field data and customer feedback, over 95 % of these valves meet or exceed operational expectations,
By Fadila Khelfaoui and Luc Vernhes
Figure 2: Worldwide deployment of Velan valves in global HPAL and POx operations.
22 Valve World August 2025 www. valve-world. net