Nitric acid treatment of carbon black

A treated furnace carbon black having properties comparable to those of channel process carbon black is prepared by thermally decomposing a hydrocarbon under conditions of free carbon formation in the presence of from 2 to 10,000 parts by weight, per million parts by weight of carbon black produced, of an alkali metal having an atomic number of at least 19, and contacting the carbon black so produced with ammonium nitrate or nitric acid to effect partial oxidation and to further reduce the modulus of the black. When using ammonium nitrate, the partial oxidation may be effected by mixing the carbon black with from 1 to 25 weight per cent of ammonium nitrate and heating the mixture at a temperature of from 155 DEG to 400 DEG C. for from 0.01 minute to 24 hours; such heating may be in the presence of from 0.01 to 5 weight per cent, based upon the weight of the carbon black, of an ammonium, an alkali metal or an alkaline earth metal halide or a mixture thereof. The ammonium nitrate, with or without such a halide, either may be added in the form of an aqueous solution to the quench chambers of the carbon black furnace or to apparatus in which the carbon black is wet-pelletized, or may be added in the form of a dry salt or salts to apparatus in which the carbon black is drypelletized. When using nitric acid, the carbon black, in either loose or pelleted form, may be intimately contacted with less than 10 weight per cent, based on the carbon black, of dilute aqueous nitric acid and heated in an atmosphere having a partial pressure of at least 0.1 atmosphere of oxygen at a temperature of from 680 DEG F. to 900 DEG F. for at least 10 minutes and until the diphenylguanidine adsorption value thereof is at least 35 microequivalents per gram of black and the volatile matter content is at least 3 weight per cent. Alternatively, the partial oxidation may be effected by wetpelleting the carbon black with 40 to 100 per cent by weight of an aqueous solution containing 1 to 25, preferably 4 to 10, weight per cent nitric acid and drying the resultant pellets at a temperature of from 250 DEG F. to 900 DEG F., preferably of from 400 DEG F. to 500 DEG F.