HPAL Process & Pexgol Applications

Posted 30 July, 2018

The HPAL process is based on the leaching of minerals, fundamentally oxidized, at high pressure (36-50 bar) and high temperature (240-270°C) using highly concentrated Sulphuric Acid (H2SO4).

Based on the technological success of HPAL technology, it has been studied by some of the world’s leading companies in its use, such as Sherritt International Corporation to extend it, not only to the extraction of Nickel and Cobalt, but also to:

Obtain in a combined way with atmospheric leaching of Ni-Cu concentrates that produce a high grade metal (PGM) for refining and obtaining Platinum.
Pressure leaching of Zinc concentrates as an alternative to the conventional roasting process.

High Pressure Acid Leaching (HPAL) and Pressure Oxidation (POX) are two of the most demanding extraction methods in the mining industry and require dependable, long-term operationally tested Pipes and Fittings. Pipes used in plants utilizing acid or oxygen injection leaching methods must withstand both corrosive and abrasive slurries as well as high temperatures and pressures.

Common pipe material selection for corrosion/abrasion resistance of the metallic pipe or coating is S.S. 316/304, duplex, titanium, and rubber lined carbon steel. These exotic materials are expensive and, in the case of RLCS, require constant maintenance.

Pexgol pipes lower both operational and capital costs by offering a field proven, plastic pipe suitable to most of the conditions in the plant pipe lines — both before the autoclave and after the flash vessel — where temperatures will normally drop below 110°C/230°C.

Pipe Material Comparison for HPAL Processes:

Material	Pros	Cons
Pexgol	Excellent corrosion resistance. Resistant to H2SO4, H2S in a variety of concentrations, and to other corrosives. Good behavior on temperatures up to 140°C (depending on the operative pressure). Good wearing resistance. Low adherence due to low superficial roughness (ideal for scale forming solutions). Good flexibility and mechanical resistance (impact, scratching). Can be supplied in lengths longer than any other competitor. Erosion can be monitored by standard ultrasonic devices.	Limited by pressure and some chemical agents and/or organic compounds (though in case of acid technology its use is very feasible).
FRP	Corrosion resistant. Temperature and pressure suitability.	Rigid pipe. Installation preparations. Short sections.
GRE	Corrosion resistant. Temperature and pressure suitability.	Rigid pipe. High price. Complex installation. Short sections.
Rubber lined steel	Can handle high pressures.	Low resistance to corrosion. Limited resistance to high temperatures (up to 92°C).
HDPE	Cheap Good resistance to corrosion.	Limited resistance to high temperature.
SS316	Good corrosion resistance. Can handle high pressures and temperatures.	High price. High installation costs and knowledge.
Duplex	Good corrosion resistance. Can handle high pressures and temperatures.	High price.
Super Duplex	Good corrosion resistance. Can handle high pressures and temperatures.	High price.
Titanium	Excellent corrosion resistance, pressure and temperature.	High price. Not good on wear conditions.

How Pexgol reduces OPEX & CAPEX:

Typically lower material cost compared to exotic alloys and RLCS.
Long term corrosion resistant to acidic conditions found in the process eliminate the need for repairs and breakdown.
Pexgol is a solid wall pipe (not a liner), so even in a case of failure, repair doesn’t require special preparation equipment as in the case of rubber lined pipe.
Durable and impact resistant – does not require special treatment such as levelling, preparation or special care as some rigid plastic pipes may require.
The energy savings can reach 20% compared to some pipe materials, increasing the system’s overall productivity.
Lightweight pipe material.
The quick install connection removes the need of welders and welding equipment – lowering skilled labor costs and risks associated with welding.
When long lines are required, the optional coiling (up to 315 mm O.D.) allows a faster installation rate and lowers risks due to fewer fittings.
The material flexibility provides installation tolerance in the field.

HPAL, Mineral Processing