Two ammonia-free acids that do different jobs. Comparing sulphamic acid and formic acid 85% for tannery deliming, pickling and descaling.
Both of these acids sit in our range, both are ammonia-free, and both will drop the pH of a float. That is where the similarity ends. Choosing between them is mostly a question of what else you want the acid to do, and how you would rather handle it.
The short version
Sulphamic acid is a solid you weigh out; formic acid is a liquid you pump. Sulphamic is the gentler, more controlled option for deliming and for descaling drums and pipework. Formic is the stronger, faster acid, and it carries a second function — it is a reducing agent as well as an acidifier, which matters in pickling, chrome tanning and dye-fixing.
| Sulphamic acid | Formic acid 85% | |
|---|---|---|
| Physical form | White crystalline solid (amino sulphonic acid), virtually non-hygroscopic when dry | Colourless liquid, 85% w/w minimum total acidity |
| Purity | 99.5% minimum, iron below 15 ppm | 85.0% w/w minimum, IS 9908:2020 Grade 2, low chloride, sulphate, iron and heavy metals |
| Handling | Weighed and dissolved; non-fuming and low odour | Pumped or dosed; the strongest of the simple carboxylic acids, handled accordingly |
| Primary tannery use | Deliming, pickling, descaling | Pickling, tanning, dye-fixing |
| Second function | Descaling — clears lime scale from drums and pipework | Reducing agent, plus natural microbial control |
| Effluent nitrogen | Ammonia-free | Ammonia-free |
When sulphamic acid is the better choice
If your problem is deliming, sulphamic acid is usually the more forgiving tool. It delimes gently, without the sudden swelling a strong acid can cause, and because it is a solid you can add it in stages and watch the pH settle rather than chase it. Two practical advantages follow from the physical form:
- →It is non-fuming and low-odour, which changes the working conditions around the drum.
- →It stores as a stable crystal and is virtually non-hygroscopic when dry — easier to keep and to freight than a drum of liquid acid.
- →The same acid clears lime scale from your drums, pipework and pumps, so one product covers a process step and a maintenance job.
Its low iron content — under 15 parts per million — also matters where iron staining is a risk on pale or aniline work.
When formic acid earns its place
Formic acid is the strongest of the simple carboxylic acids, and there are stages where you want that. In pickling and chrome tanning it brings the float down quickly and reliably, and because it is also a reducing agent it does work no solid acid will do for you. It fixes dye, and its natural microbial control restricts spoilage in the float — a real benefit in warm conditions on long process times.
Low chloride, sulphate, iron and heavy-metal content keeps it clean going into a chrome bath, where trace contamination shows up later as uneven colour.
Using both
Most tanneries we supply end up carrying both, and split them by stage rather than choosing one. A common pattern: sulphamic acid through deliming, where control matters more than speed and the descaling benefit is a bonus; formic acid from pickling onward, where you want strength, a reducing action and clean chemistry into the chrome bath.
If you are moving away from ammonium salts, note that both routes are ammonia-free — so is DELIME-A, our dedicated ammonium-free deliming agent. We wrote about that trade-off in ammonium-free deliming.
What to send us
Tell us the stage you are treating, your hide or skin volume per batch, and the acid you are running now. We will tell you honestly whether a change is worth it — sometimes the answer is that your current acid is fine and the problem sits elsewhere in the process. Data sheets for sulphamic acid and formic acid 85% are available on request.