Abstract: A waste material which contains chromium and/or lead impurities is treated by mixing the waste material with diatomaceous earth and/or sodium borate and then heating the mixture in a free oxygen containing gas at about 500.degree.-1500.degree. C., preferably in the presence of steam.

Abstract: In a crude oil refining apparatus, heavy cycle oil from the catalytic cracking unit employed in the crude oil refining apparatus is recycled to a hydrofining process. Such recycling improves the value of the product mix obtained from the crude oil refining apparatus with respect to an apparatus in which the heavy cycle oil withdrawn from the catalytic cracking units is recycled to the catalytic cracking units.

Abstract: In a crude oil refining process, heavy cycle oil from the catalytic cracking unit employed in the crude oil refining process is recycled to a hydrofining process. Such recycling improves the value of the product mix obtained from the crude oil refining process with respect to a process in which the heavy cycle oil withdrawn from the catalytic cracking units is recycled to the catalytic cracking units.

Abstract: A process is provided for reducing water production in production oil wells or for altering the water permeability profile of injection wells that have been previously treated with partially gelled or ungelled polymer and from which oil has been produced for a period of time subsequent to the treatment. The retreatment is made by injecting into the formation an ionic solution capable of crosslinking residual ungelled polymer in the formation and thereafter injecting into the formation an aqueous solution of polymer capable of being crosslinked by the ionic solution. In a preferred embodiment aluminum citrate is injected into an underground formation that has previously been treated with an ungelled polymer selected from among polyacrylamides, partially hydrolyzed polyacrylamides, polysaccharides, carboxymethylcellulose, polyvinyl alcohol, polystyrene sulfonates, and the like, with the aluminum citrate being followed with a solution of an at least partially ungelled polymer selected from those above named.

Abstract: A method is provided for plugging an underground formation in which a composition of water, a polymer capable of gelling in the presence of a crosslinking agent, and a crosslinking agent capable of gelling the polymer are injected into an underground formation with maintenance of the pH in the underground formation within the range of about 3 to about 7. In an embodiment of the invention plugging of the underground formation can be removed by decreasing the pH in the formation below 3 or increasing the pH in the formation above 7.

Abstract: A method is provided for obtaining good residual resistance factor at relatively low ratios of crosslinking agents to polymer for plugging fractured or porous media using a method of injecting into the formation a first aqueous polymer solution followed by an injection of crosslinking agents capable of gelling the polymer solution and thereafter injecting a second aqueous polymer solution that is capable of being gelled by the crosslinking agents. In each of the aqueous polymer solutions the polymer is already partially crosslinked before the polymer solution is injected into the formation. This process is applicable to production wells and injection wells.