Done some research for you not sure if this is the same stuff I used years ago but this ones main use it for rust.
Oxalic Acid
Oxalic acid's main applications include cleaning or bleaching, especially for the removal of rust (iron complexing agent, e.g. Bar Keepers Friend is an example of a household cleaner containing oxalic acid. Its utility in rust removal agents is due to its forming a stable, water soluble salt with ferric iron, ferrioxalate ion.
Toxicity and safety
Oxalic acid has toxic effects through contact and if ingested; manufacturers provide details in Material Safety Data Sheets (MSDS). It is not identified as mutagenic or carcinogenic; there is a possible risk of congenital malformation in the foetus; may be harmful if inhaled, and extremely destructive to tissue of mucous membranes and upper respiratory tract; harmful if swallowed and causes burns; harmful, destructive of tissue and causes burns if absorbed through skin or in contact with the eyes. Symptoms and effects include burning sensation, cough, wheezing, laryngitis, shortness of breath, spasm, inflammation and oedema of the larynx, inflammation and oedema of the bronchi, pneumonitis, pulmonary oedema.[15]
In humans, ingested oxalic acid has an oral LDLo (lowest published lethal dose) of 600 mg/kg.[16][dead link] It has been reported that the lethal oral dose is 15 to 30 grams.[17]
The toxicity of oxalic acid is due to kidney failure, which arises because it causes precipitation of solid calcium oxalate,[18] the main component of kidney stones. Oxalic acid can also cause joint pain due to the formation of similar precipitates in the joints. Ingestion of ethylene glycol results in oxalic acid as a metabolite which can also cause acute kidney failure.
Just remember the safety side of it.It is an acid and just treat it with the greatest of respect and it will do this job for you.
I've also been reading a lot about vinegar for rust removal,but I don't think that will help at this point maybe a bit to far gone for vinegar to help now.
Hope this helps you out.
