Provided is a process for recovering metals from solid radioactive waste, preferably uranium, cesium, mercury, thorium, rare earths or combinations thereof. The process comprises a leaching step and a separation step. The leaching step comprises contacting the solid radioactive waste with an aqueous inorganic acid and a leaching salt to produce a mixture of a metal-rich leachate and a metal-poor waste, which are separated in the separation step. Also provided is a process for recovering metals from solid radioactive waste comprising an attrition step, a leaching step, a washing step, a combination step and a recovery step.

The invention relates to a separation and recovery method for radioactive waste slag and specifically relates to a separation and recovery method for monazite slag. The separation and recovery method comprises the following steps: acid leaching, pressure filtration, water washing, extraction of valuable components and treatment of filtration slag. The separation and recovery method provided by the invention performs low-acid and low-temperature leaching on monazite slag, so that a liquid phase and a solid phase are easy to separate; after an ore dressing process is adopted for performing ore dressing and alkali decomposition on secondary slag, closed-loop circulation and recovery of uranium, thorium and rare earth is realized; and simultaneously, extraction raffinate waste acid is recycled, so that the emission of waste water is reduced, the consumption of sulfuric acid and fresh water and the treatment cost of the waste water are reduced, the production cost is reduced, the recovery rate of the valuable elements, namely the uranium, the thorium and the rare earth is more than 97%, and the whole process has no emission of the radioactive waste water and waste slag.

Disclosed herein is a method for recovering an acid or a base during a metal extraction process. The method comprises contacting a feed stream comprising the acid or base and the metal with an ultrafiltration membrane to produce an ultrafiltration retentate and an ultrafiltration permeate, and contacting the ultrafiltration permeate with a nanofiltration membrane. The nanofiltration retentate produced comprises a majority of the metal from the feed stream, and the nanofiltration permeate produced comprises a majority of the acid or base from the feed stream. Also disclosed herein is a recovery apparatus for recovering an acid or a base during a metal extraction process.

The present invention relates to a method for irrigating a porous substrate comprising the steps of: preparing a foam consisting of a dispersion of air bubbles in a foaming aqueous solution, said foam comprising a liquid fraction of less than or equal to 15% by volume; spreading, over the surface of the porous substrate, a layer of the foam thus prepared, the thickness of the layer being greater than 5 cm, then maintaining the assembly long enough for at least a part of the liquid contained in the foam to infiltrate the porous substrate. The present invention also relates to the use of this method to recover an element of interest contained in a porous substrate and a particular aqueous foam.