To depreciate or not to depreciate that is the question! Whether...

To depreciate or not to depreciate that is the question! Whether 'tis nobler in the mind to suffer The slings and arrows of outrageous fortune, Or to take arms against a sea of troubles And by opposing end them.
(Apologies, couldn't help myself!)

So they built the LAMP and, like most companies, they put the cost as a liability on the balance sheet.
Depreciation usually occurs over a big fraction of the asset's working life. A part of the liability is transferred to the profit/loss each year lessening both the liability and taxable income.
In view of the expected closure of the LAMP's cracking and leaching, it made sense to accelerate the depreciation of that asset. You don't really want unproductive liabilities on an otherwise extremely healthy balance sheet. And preserves as much cash flow as possible in times of massive expansion.
All makes sense to me as basic, prudent management on the part of Lynas.

So is the loss of local sulphuric acid a big deal? To quote Wiki:
Sulfuric acid is a very important commodity chemical, and indeed, a nation's sulfuric acid production is a good indicator of its industrial strength. World production in the year 2004 was about 180 million tonnes, with the following geographic distribution: Asia 35% ... Australia and Oceania 7%...

Maybe it's an opportunity down the track to make our own. You basically need sulphur and water with the S about 1/3 of the final chemical's weight.
Sulphur is also a mild and easily transported powder. Basically, you just have to burn it (generates heat too) then add water. There's some machinery involved too of course!