Abstract: Hydrogen fluoride production apparatus removes phosphate rock dust from a hot gas mixture exhausted from a phosphate rock defluorination kiln; cools the hot gas mixture in a heat exchanger to a low enough temperature that it can be brought into contact with acid-resistant polymeric materials without destroying them; uses a water spray scrubber for further cooling the gas and absorbing the fluoride values as HF-rich liquor; and pumps the HF liquor to a holding tank. One such plant uses a gas tube steam boiler as the heat exchange and has several series-connected scrubbers to extract the fluorine values from the kiln exhaust so that the residual gas mixture can be exhausted into the atmosphere without exceeding permissible fluorine value levels. In this arrangement water is fed into the scrubber furthest from the boiler to extract HF from the process gas, and an HF-laden process liquor is fed out of the furthest scrubber into the second furthest scrubber, where it is sprayed into the gas stream.