Abstract: In a process of cleaning metal surfaces with aqueous alkaline cleaning solutions, which contain silicates and surfactants and are recycled after ultrafiltration, a solution is employed which contains silicate only as a sodium silicate and/or potassium silicate of the formula Na.sub.2 O.2SiO.sub.2.xH.sub.2 O and/or K.sub.2 O.2SiO.sub.2.xH.sub.2 O. The cleaning solution is preferably adjusted to a pH value between 7 and 12 and to a concentration (expressed as SiO.sub.2) of 0.1 to 20, particularly 0.5 to 10 g, silicate per liter.

Abstract: A process for forming phosphate coatings on metal surfaces is provided which comprises the steps of contacting said metal surface with an Fe(II)-containing phosphating solution comprising0.4 to 30 g/l Zn4 to 30 g/l P.sub.2 O.sub.55 to 50 g/l NO.sub.3up to 10 g/l Fe(II) ; andup to 0.3 g/l (Fe(III)wherein the weight ratio of free P.sub.2 O.sub.5 to total P.sub.2 O.sub.5 is (0.04 to 0.50):1 and, replenishing said phosphating solution with Zn, NO.sub.3 and P.sub.2 O.sub.5 in a weight ratio ofZn:NO.sub. 3 P.sub.2 O.sub.5 =(0.60 to 0.30):(0.2 to 0.4):1.wherein the Fe(II) content is adjusted by oxidation with nitrate or nitrite derived from nitrate optionally employed with an oxygen-containing gas, H.sub.2 O.sub.