The present publication describes a process for the preparation of lignosulfonate-based mixtures used in particular as additives of concrete. According to the process of the present invention, the sulfite spent liquor is treated with a nitrating reagent, such as nitric acid or nitrogen dioxide, and the reacted lignosulfonate is separated from the reaction product, and, together with the reacted lignosulfonate, the nitrate and nitrite compounds are separated from the reaction product, and the product mixture formed by the reacted lignosulfonate, nitrate compounds and nitrite compounds is purified in a way known per se. The product prepared in accordance with the process is suitable in particular for the liquefaction of concrete, for accelerating the setting of concrete, and for inhibiting corrosion of concrete reinforcement steels contained in concrete, if any.