Currently chlorine is not renewable from what i gather, i remember when playing GTNH you could get some from ghast tears, since DML facilitates the gathering of tears maybe a recipe to turn them into chlorine either directly like 4 ghast tears into 1b of chlorine or something like 4 tears plus water turns into 2b of salt water then the salt water can be processed into salt and from salt you get the chlorine.

We can create one with multiblocktweaker
also holy crap this issue is old; exactly what I'm looking for

When this issue was first opened Chlorine was a pain largely because of the Titanium processing loop being lossy. This had side effects like making players avoid EV tier machinery like the plague.

With the fix zip changes to Titanium processing that were added into 1.2.2, and later canonization into the versions of GTCE we're using in dev snapshots (thus will be in 1.3), the most significant chlorine sink no longer exists.

Additionally, GTCE chemistry has been carefully reviewed and standardized so you get the right ratios of all processes, meaning you can no longer exploit salt water to double the yield, but also that you're not going to effectively void Chlorine in various processes.

Given that Chlorine is easily accessible via buying a bit of salt with Omnicoins and scanning for a salt vein in the early game, then later infinitely renewable from Micro Miners, it doesn't really seem that there is a need for other ways to make salt.

Currently chlorine is only obtainable from salt, which can be either coin-bought or micromined. A pre-microverse recipe might be useful, especially since the microminer recipe is one stack of ore per launch.

I think we can just make salt be a DML product, perhaps from thermal elementals or guardians (you could justify this by the fact that they live in a salty ocean? Well i guess there is not way to justify copper from spiders so...).

The distillation tower might be a good way to make salt, because you can have an item output, but only one and making salt should be pretty renewable

I'd suggest the Mekanism way of using thermal evaporation to turn water into brine, and then crystallising brine into salt, if we're going for some kind of distillation of water. However, really, I prefer the sound of the ghast tear approach. Perhaps they could be fluid extracted into saltwater?

we got to see if GTCE has a thermal evaporation plant or somehing like that

getting it from water is way to easy that's why i said getting it from salt water and give salt water a recipe from water and tears, that way you at least have a couple more steps to make and it gives ghast tears a good use which at the moment it doesn't have.

Maybe a multiblock that turns water into salt?

Maybe make the Distillation tower give salt as a byproduct of distilling water. But that would conflict with the salty water recipe wouldnt it.

Perhaps 3B hydrocloric acid with 1B salt water [in a MV+ chemical reactor?] to give 1B Chlorine along side 2B Hydrogen 3B Oxygen as by-product? or something similar