LIQUID WASTE-FREE METHOD FOR MANUFACTURING PHOSPHATE COATINGS ON METAL SURFACES

In a process for the production of phosphate coatings on metal surfaces by means of aqueous zinc phosphate solutions containing iron(II) and nitrate ions, it is possible to work in the absence of waste water if the metal surfaces are brought into contact with an aqueous phosphating solution which contains 0.4 to 30 g/l of Zn, 4 to 30 g/l of P2O5, 5 to 50 g/l of NO3, not more than 10 g/l of Fe(II) and not more than 0.3 g/l of Fe(III), in which the weight ratio free P2O5 : total P2O5 is (0.04 to 0.50) : 1, which is supplemented with Zn, NO3 and P2O5 in a weight ratio of Zn : NO3 : P2O5 = (0.60 to 0.30) : (0.2 to 0.4) : 1 and in which the Fe(II) content is established only by oxidation with nitrate, nitrite formed therefrom, optionally together with oxygen-containing gas, H2O2 and/or nitrous gases. A rinsing bath cascade comprising at least two rinsing baths is located downstream of the phosphating bath, water which has a low salt content, preferably salt-free water, is fed into the last rinsing bath, viewed in the direction of workpiece flow, the water overflow is passed into the preceding rinsing bath in each case or into the phosphating bath, and water having a low salt content or salt-free water is removed from the phosphating bath at least in an amount such that the said phosphating bath can hold the phosphate-enriched rinsing water from the cascade.