Franglais:
Dont all ADR tanks need Type Approval, Certification, periodic checks? Not the sort of thing you
d “pick-up” anywhere.
Indeed, correct on all accounts; to paraphrase Sheryl Crow “This ain’t no disco, it ain’t no country club either, This is A-D-R” 
Both tank and vehicle need to be constructed to ADR specifications.
the tank needs to have a certificate of conformity. This will do you for the first 12 months, after this the tank must be tested by the competent authority and obtain an ADR1(C) certificate, the tank manufacture plate then gets marked with periodic test date
Every tank undergoes regular testing and inspection
Fixed tanks: periodic (full) test every six years, intermediate (less detailed) test every three years,
Removable tanks are respectively 5 (periodic) and 2.5 years (intermediate)
As well as this the vehicle, or vehicle plus trailer, needs to be tested (ADR IIIS) to get a Vehicle Approval Certificate (VAC), I refer to these as an ADR MOT because you need one every 12 months, and it makes sense to get both MOT and VAC done at the same time because its the same people (DVSA) who do these inspections/tests. If it’s a rigid you only need one, for an artic plus trailer you need one VAC for each.
As if all that isn’t enough, the driver obviously needs to be ADR trained and other staff need basic awareness training, the operator needs to secure the services of a DGSA, and then there’s all the rest of the stuff that goes with ADR: extra fire extinguishers, placards, orange plates, UN Numbers, Emergency Action Codes, PPE kit bag etc etc.
I don’t know why the OP has specified aluminium tanks, if he’s looking for a removable tank then I can’t see that the weight saving of aluminum is worth much when you need the ISO frame for the tank to sit in,which will obviously be steel not ally.