Contact between the metal 一 containing solution and the proteinaceous material mateial may be continuous or batchwise. In a batch type operation，the dosage of proteinaceous material may be within the range of 1 to 20 weight percent based on the weight of the aqueous solution. A preferred method of operation involves continuous countercurrent contact between the aqueous solution and the proteinaceous material. In one preferred embodiment of a continuous countercurrent contacting method of operation, the proteinaceous material is contained in a series of stationary beds. An apueous aqueous solution containing dissovlved metals is passed through the series of stationary beds of proteinaceous material，contacting first a bed of material nearly saturated with respect to recovered metal values，then a bed containing a lesser amount of recovered metals，and so on until the last bed contacted is essentially barren of recovered metal，or substantially a fresh bed proteinaceous material. As the first bed becomes loaded with metal，the flow of aqueous solution is switched to the next and a fresh bed of proteinaceous material is added to the final contact with the aqueous solution. In a similar manner，aqueous solutions may be successively passed through a series of contacting zones which are stirred or agitated or maintained in a fluidized solids bed condition. All of these systems are well known in the arts of solvent extraction， water treatment，and the like.
Altemaively，successive batches of fresh，i. e. untreated, solution may be brought into contact with a batch of solid proteinaceous material, preferably in a reactor containing a stirrer or other appropriate means of agitation, and the batch processing continued until the proteinaceous material becomes loaded with metal when the effectiveness of the proteinaceous material for metal recovery is substantially diminished due to loading with metal, it may be removed from the reactor and processed for recovery of metal values. Fresh or regenerated proteinaceous material is charged to the reactor to replace the loaded material removed therefrom. A series of two or more batch reactors may be employed in which treated aqueous liquid from one reactor is supplied as the aqueous liquid feed to another reactor. The second or any subsequent reactor may contain the same or a different proteinaceous material from that of the first or precedent reactor，the proteinaceous material in the second reactor having a lesser degree of metals saturation than that in the first reactor，and so on. Such a procedure applies the countercurrent principle of metals removal, as described above，to a metal solution successively exposed to a series of batch contact reactors, each containing a different batch of proteinaceous material. In a batch type operation, the relative proportions of proteinaceous material to solution may be within the range of 10 to 500 grams per liter of solution ，preferably in the range of 50 to 200 grams per liter，where the proportion of added proteinaceous material governs the rate of metals removal and the time to achieve either substantial metal removal or saturation of the proteinaceous material.
In accordance with one aspect of the present invention，the metal values are recovered from the proteinaceous material containing the precious metals extracted from an aqueous solution by physical separation of the proteinaceous material from the solution，followed by extraction of the metal values from the proteinaceous material. Extraction of metal values may be accomplished by drying and complete oxidation of the organic matter in the proteinaceous material whereby the precious metal remains in the ash as a solid residue. Metal values may be recovered from either the metal - containing proteinaceous material or its ash by any of various known refining methods. For example, the metal values may be recovered by redissolving the metal in a concentrated mineral acid，such as hydrochloric acid or nitric acid, and the metal values recovered from the concentrated solution in known manner. The accompanying drawing is a diagrammatic representation of a preferred embodiment of the process of this invention.
With reference to the drawing, a multistage process is illustrated utilizing three reactors or contactors in series. It is to be understood that the principles of this invention apply regardless of the number of reactors or contact zones in the plant design. A plurality of contactors are illustrated and are designated by the letters A, B, C, I), and A ’ . A and A ’may be the same contactor in different stages of operation. As illustrated，Reactors B, C, and D are in service removing metal values from aqueous solutions containing dissolved metal salts, for example, water from a precious metals refinery. Reactor A is in the process of recharging fresh proteinaceous solid and Reactor A ’is discharging loaded proteinaceous solid material for further treatment to recover the metals removed from the metals solution.
A suitable proteinaceous solid, such as fresh, wet chicken feathers ，is charged into Reactor A through line 2. The reactors may be identical in construction and preferably are of the fixed bed type. As illustrated, the aqueous medium undergoing treatment passes downwardly through the beds of solid proteinaccus material, although either upflow or downflow, or even horizontal flow may be employed in process.
Aqueous solution containing metals in ionic form, i. e. metals in solution, enters the system through line 6 where it may be passed through heat exchanger 7 to heat or cool the solution to the desired contacting temperature. The aqueous solution, e. g. refinery waste water, is introduced through line 8 to the upper portion of Reactor D of the and passed downwardly through the bed of proteinaceous material, for example，wet chicken feathers，contained in the reactor. The treated liquid, substantially from entrained solids，is discharged from the lower portion of Reactor D and passed through line 9 to the upper portion of Reactor C. In Reactor C，the water containing residual metal values not removed by the proteinacerial in Reactor D again contacts a bed of proteinaceous material in Reactor C，effecting farther removal of metal values from the aqueous liquid feed stream. The treated liquid from Reactor C，in turn, is discharged from the lower potion of Reactor C through line 11 and introduced into the upper portion of Reactor B containing a relatively fresh bed of solid proteinaceous material. Treated water, depleted in metal ions，is discharged from the lower portion of Reactor B through line 12 and may be passed through heat exchanger 7 and then through line 13 for disposal or recirculation to the process from which the solution was derived.
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