High density, high stability, sized metal oxide powder and process for making same

The present invention relates generally to a novel approach to treating spent pickling acids, and a useful product resulting from such treatment or recycling approach. More specifically, the present invention is directed to compositions of matter of a high density, high stability, high absorption capacity composite metal oxide preferably comprising designed ratios of iron oxide and zinc oxide from inexpensive, waste raw materials such as, spent hydrochloric galvanizing pickling acids. Further, the present invention describes a process for reacting the spent pickling acids with an alkali hydroxide, oxide or carbonate to generate an alkali chloride and a mixture comprising iron and zinc oxides and hydroxides. The product of the reaction is then filtered, and the content of the alkali in the solids is adjusted according to application requirements, after which the solids are calcined and then screened to a required particle size. One beneficial application of the composite metal oxide of the present invention is its use as a drilling fluid weighting agent.