Apparatus (10) for treating a waterway having low pH and containing metals
such as aluminium in solution, as a result of runoff from acid sulphate
soils, is capable of dosing the waterway with a variety of reagents, to
bring the metals out of solution and to achieve a neutral pH. The
apparatus (10) includes a rotating drum tumbler (14) having a cylindrical
drum (52) which, as it rotates, causes limestone rock to abrade to
produce particles of calcium carbonate with which the waterway may be
dosed. The inner surface of the drum (52) is provided with an abrasive
surface (68) which contacts rock pieces (74) and transports them within
the drum (52) as the drum (52) rotates, and with guide vanes (72) which
contact and deflect the rock pieces (74), causing the rock pieces (74) to
abrade each other. Other reagents in liquid and/or powder form may also
be dispensed.