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The paper describes the preliminary researches on the influence of the ultrasounds of diversified intensity (22 and 24 kHz) on the content iron compounds in water. For the researches, variable operational parameters were used, such as: the vibration amplitude and the exposure time (1–5 min). The substrate was: distilled water and natural river water of intensive colour, prepared by iron Fe(II) compounds (iron ammonium-sulphate). The effect of ultrasounds was researched as a result of the influence of sonochemical oxidation processes and ultrasound coagulation on iron in the ionized form (of ions Fe2+) and on iron–organic complexes in the lowionized or colloidal form. The share of sonochemical and coagulation processes depends on the parameters determining the ultrasounds intensity. The effects of the iron removal were researched at the low and high intensity determining the strain of cavitation processes. As a result, the changes of iron content (Fe2+, Fe3+, Feog) and the colour of water exposed to ultrasound field of variable parameters were presented. The effectiveness of the researched processes was analysed from the point of view of the possibility of determinate intensity ultrasound usage as an unconventional method of the removal of iron from water.

The results presented in this paper show that • Ultrasounds of the frequency 22 and 24 kHz initiate phenomena influencing iron(II) oxidation in water. The separation of the oxidized form Fe(III) enables the decrease of the general content of iron. • The intensity of the sonochemical effects of iron oxidation was greater at the use of more intensive ultrasound field. The increase of the effects in the removal of iron from water was assumed with the elongation of the time of sonification up to 5 min and the vibration amplitude up to 54 μm. The maximum effectiveness of the researched process was at the level of 30%. • The effect of ultrasounds on the removal of iron compounds was also proved in natural water conditions. The decrease of the content of iron combined with humic acids was noticed. The decrease of colour, turbidity and oxidity was equivalent to the removal of 0.75 mg Fe/dm3 (at low intensity) and 1.70 mg Fe/dm3 (at high intensity). • The oxidation of soluble iron–organic complexes — from Fe(II) (mainly determining water oxidity), is more intensive at higher ultrasounds intensity. At the use of the ultrasounds of low intensity, more effective is destabilization and removal of colloidal iron compounds which influence water turbidity.