DD293142A5 - METHOD FOR RECOVERING PALLADIUM FROM WAESSRIG SOLUTIONS - Google Patents

Abstract

The invention includes a process for the recovery of palladium from aqueous solutions (wastewater), especially the electroplating industry. The essence of the invention is that the liquid membrane process is used with an azathiaalkane as carrier and, moreover, the liquid membrane consists of hydrocarbons, preferably of alkanes of chain length C12 to C18 and a suitable oelloesic surfactant. The inner aqueous phase contains diethylamine as reagent. From the inner phase, after completion of the transfer of the palladium and the separation of the emulsion, the palladium is recovered by adding hydrochloric acid and ethanol as palladium chloride. Palladium; Sewage; Electroplating industry; Azathiaalkan; Mono-bis-succinimide; diethylamine; Hydrochloric acid; Hydrocarbon}

Description

R ¹

where n, m and o can be 1 to 4, preferably 2, and R, R ¹ and R ^{2 are} aliphatic radicals with chain lengths C ₄ to Cs, used singly or in a mixture, and otherwise the liquid membrane of hydrocarbons, preferably alkanes of chain length C ₁₂ to C ₁₈ and a suitable oil-soluble surfactant.

2. The method according to claim!, Characterized in that the organic membrane phase consists of more than 90% of hydrocarbons, preferably an alkane mixture of chain length Ci ₂ to Ci ₈ , and in addition to the carrier, a soluble surfactant, preferably mono-bis-succinimide contains.

3. The method according to claim 1, characterized in that the volume ratio of external phase to be separated to the inner receiving aqueous phase 10 to 1 to 200 to 1, the volume ratio outer aqueous phase to the organic membrane phase 5 to 1 to 20 to 1, the volume fraction of the carrier in the membrane phase is 0.02 to 0.04 part by volume and that of the surfactant is 0.01 to 0.04 part by volume and in the inner phase the concentration of diethylamine as the reagent is 0.001 to 0.01 part by volume.

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Field of application of the invention

The invention relates to a process for the separation and recovery of palladium ions from aqueous solutions, in particular from wastewater. Thus, the invention is useful for both reducing the environmental impact of palladium and recovering this valuable metal. The preferred field of application of the invention is the recovery of palladium ions from the waste water of galvanic plants and the printed circuit board industry.

Characteristic of the known state of the art

The removal of low level metal ions from aqueous solutions can be accomplished by various methods, particularly by precipitation, liquid-liquid extraction including back-extraction, ion exchange, reverse osmosis or ultrafiltration, and the liquid membrane process. In this case, precipitation processes always have the disadvantage of a high demand for chemicals and time-consuming and labor-consuming filtration operations and in many cases do not allow the necessary for economic or environmental reasons, depletion of residual levels in the ppm range. Ion exchange, ultrafiltration or reverse osmosis are not applicable in particular if solid components are present in the solution. The liquid-liquid extraction followed by back-extraction involves two process steps with a considerable need for reagent and organic solvent. These extraction methods have the disadvantage, especially at low value metal contents, that the cost-benefit ratio deteriorates drastically. Solid ion exchangers that take up palladium can not be regenerated. The valuable ion exchanger must therefore be ashed to recover the palladium after loading. The reverse osmosis or ultrafiltration with solid membranes can only be applied if the solid

Membranes are sufficiently selective and there is a low tendency to block the membranes. For the separation of low-concentration palladium, solid membranes are not effective enough. These disadvantages are avoided when using a liquid emulsion process with multiple emulsion. Decisive for the applicability of this method for the separation of valuable metals from aqueous solutions is the use of a selective as possible complexing agent, called carrier, with sufficiently fast kinetics of complex formation with respect to the metal of interest. Further requirements are for a circulation process sufficient absorption capacity for the metal in the inner phase and favorable opportunities for recovery. For the task of recovering palladium from aqueous solutions by liquid membrane technology so far there are no known technical solutions, because obviously no the given technological and economic requirements sufficient carrier was found.

Object of the invention

The aim of the invention is to provide an economically favorable process for the production of palladium with a concentration of a few grams per cubic meter of water, in particular for wastewater, by which the palladium at least 95% removed from the aqueous solution and in another aqueous phase so enriched that with little effort, the palladium can be recovered.

Explanation of the essence of the invention

The invention has for its object to provide a process for the recovery of palladium from aqueous solution, which allows an economically favorable removal and recovery of at least 95% of the palladium contained in the aqueous solution (usually wastewater).

According to the invention the object is achieved in that a liquid membrane process with a liquid membrane with a novel carrier, the Azathiaalkan the general formulas 1,2,3 or 4

^R1

Formula J, for example

C ₄ H ₉ -

R '

Formula 2 for example

^{N is} N- (0H ₂ ) ₂ -S- (CH ₂ ) ₂ -I

R ¹

RS (CH ₂ ) _n formula 3

for example

C ₄ II ₉ -S- (CH ₂ ) ₂ »N

/ (CH ₂ ) _n ( ₂ ) _m ( ₂ ) _o -W ^ ^{2 R}

Form I 4 _n vr

° 4 9. / ^{4 9}

for example ⁿ W ~ (CH _{2) 2} -S- _{(CH?) 2} ~ S- (CB _{2) n} -N ₂

^C 4 ^H / ° 4 ^H 9

and, moreover, the liquid membrane consists of hydrocarbons, preferably of alkanes of chain length Ci ₂ to C ₁₈ and a suitable oil-soluble surfactant. The liquid membrane consists of the novel carrier, preferably with 0.02 to 0.04 part by volume, a soluble in the liquid membrane surfactant, preferably 0.01 to 0.04 part by volume and hydrocarbons as the remainder, preferably alkanes of chain length C ₁₂ to C. ₁₈ , which are insoluble in water. As the surfactant, for example, a mixture of mono-bis-succinimide can be used. The liquid membrane composed according to the present invention ensures that the outer continuous phase (starting solution) and the inner disperse phase do not directly contact each other, so that the palladium ions are effectively transferred and enriched by the carrier from the outer phase through the liquid membrane into the inner phase can be. The inner phase contains a complexing agent, which causes the return of the metal in this aqueous phase. Suitable compounds are ammonia or water-soluble alkviamines such as diethylamine. After appropriate loading of the inner phase, the palladium can be obtained as palladium chloride in a known manner by the addition of hydrochloric acid and ethanol.

embodiment

The embodiment is shown in the form of a schematic diagram in Fig. 1 and will be described below. It is the palladium with a concentration of 10 grams per cubic meter of water to be removed from the wastewater of a galvanic plant. The inner phase should be enriched to about 980 grams of palladium per cubic meter of water. The modern technical design of the liquid membrane process consists of three process stages. In a Tropfenrührkolonne 1, the waste water is supplied in consideration of the density differences in the upper cylindrical portion and in the lower part of the column, the emulsion consisting of the membrane phase and inner phase supplied. The membrane phase typically consists of 0.95 parts by volume of n-alkanes of chain length C ₁₂ to C ₁₈ , 0.03 part by volume of dithiamonoazaalkane as carrier and 0.02 part by volume of mono-bis-succinimide surfactant. By means of rotating internals in the droplet-stirring column, for example blade-type agitators arranged on a shaft, the dispersion consisting of the outer continuous phase (waste water) and the macrodrop consisting of the membrane phase and the inner phase is maintained. The uppermost part of the droplet-stirring column is dilated to promote the separation between the outer aqueous phase and the macro-droplets which coalesce. Likewise, the lowermost part of the droplet stirring column is widened to prevent entrainment of macrodrops with the effluent effluent.

In the demulsifier 2, the emulsion is separated into the membrane and inner aqueous phase by means of an electric field. The electric field is very effective with a frequency of 10 to 25 kHz at a voltage of at least 1000 volts. The necessary device is simple and reliable. In an emulsifier 3, the membrane phase is emulsified with fresh inner phase by means of the surfactant dissolved in the membrane phase. For the emulsifier, machines with shear stress or an apparatus with nozzles are particularly effective. For the present material system, a contact time of 10 minutes is appropriate for the emulsification.

The containers 4 and 5 and the pumps 6 and 7 complete the technical solution. The volume ratio for the present task is chosen to be outer phase V ₃ to inner phase Vi as 100 to 1 to achieve at least a 98-fold enrichment of the inner phase with palladium. It has been proven to choose a ratio of external phase V ₃ to organic phase V ₂ of 10 to 1. This results in the present task V ₃ IV ₂ IV ₁ = 100: 10: 1.

The inner phase contains 0.004 part by volume of diethylamine. The palladium-diethylamine complex formed by the incorporated palladium can be decomposed by addition of hydrochloric acid and ethanol, whereby palladium chloride precipitates. This palladium chloride can be newly used in the process of galvanization.

Claims (1)

1. A process for the recovery of palladium from an aqueous solution by a liquid membrane process, characterized in that as a carrier in the liquid membrane Azathiaalkane of the general formulas 1 to 4, R ¹ R ¹ N- (CH ₂ ) _n -SR
1