In battery recycling leaching, why do instruments fail so quickly?

Conclusion first

Instruments in the leaching section are rarely “used up” — most fail because of wrong material selection and wrong sampling design. Fluoride-bearing strong acid, chloride, solid particles and temperature cycling act together; leave any one unaddressed and instruments fail within months.

Four stacked failure mechanisms

Mechanism	Trigger	Typical symptom
Chemical corrosion	Sulfuric, hydrochloric, hydrofluoric acid	Wetted parts thin out; seals fail
Chloride pitting	Chloride systems	Pinholes in stainless; sudden perforation
Abrasion	Solid-laden slurry, agitation	Measuring-cell wear, wall grooves
Thermal cycling	Heated leaching alternating with cooling	Lining delamination, flange leaks

The destructive power of fluoride is often underestimated: it attacks not only metals but also glass-like parts (including the pH electrode’s glass membrane). In fluoride service, ordinary glass electrodes fail far sooner.

Material selection logic

• Fluoride-bearing strong acid: prefer non-metallic wetted parts (PVDF, PTFE etc.) and keep metal ions out of the system
• Solid-laden slurry: minimize dead zones and throttling inside the cell; prefer straight-through structures
• Hot sections: separate continuous from peak temperature and size against the peak
• Seals: confirm material compatibility separately; never assume it follows the valve body

Sample conditioning often matters more than the instrument

Leachate carries solids, gas and heat. Sending it straight to the instrument causes three problems: blockage, bubble interference, temperature overrun. The standard practice is four steps — cool, depressurize, de-solids, de-gas — skipping any one hands the problem to the instrument.

When it is not the instrument’s fault

• Process swings themselves exceed the range
• Sample point poorly located (dead zone, bubble zone)
• Cleaning and calibration intervals not executed
• No spare or consumable stock — a failure stops the line

How to implement

Start with a medium list: acid type and concentration, fluoride content, chloride content, solids content, temperature range, pressure. Only with all six can selection be discussed. With any item missing, writing “select per actual duty” is more responsible than quoting a number.

For lines already in operation, improving sample conditioning and flushing usually beats buying a more expensive instrument.

Spares strategy

Instruments in leaching are high-consumption items; stock them above the usual ratio. Track failure intervals and hold roughly half a year of consumables (electrodes, diaphragms, seals, sample pump tubing).

A pragmatic rule

If the same point has been replaced more than three times in a year, the selection or sampling design is wrong — replacing the same model again just repeats the cost. Redo the duty assessment instead of enlarging the spares stock.

Coordination with process

Leaching acidity, temperature and solids get adjusted regularly. Every process change should trigger an instrument-suitability review — a step skipped in most projects.