CS256980B1 - Method of platine regeneration of bipolar electrolyzers' polyvinyl chloride membranes - Google Patents

Abstract

A method for regenerating platinum from PVC membranes of bipolar electrolysers to make ammonium peroxodisulfate or acid peroxodisulfate rests on the elution of platinum for three hours using a boiling royal kings acting on membranes rolled into a spiral and embedded in a glass a vessel fitted with a reflux condenser. Maxim elution is achieved with the elution module 2.2 1 / kg. To reduce the acid content sulfur and lead in the extract is preceded balancing membranes with nitric acid 10% by weight. To reduce loss of platinum by mechanical fatigue of the extract Water Balancing is included in a ratio of 2.2 1 / kg membranes. Precipitation in chloroformate is carried out from extract and water broth by solid chloride ammonium hydroxide at 50 g / l for the presence of ethyl alcohol in such quantities, to produce a concentration of ethyl alcohol 30% by volume and subsequent flushing concentration of the precipitate on the filter with ethyl alcohol 50% by volume. Chloroplatinate obtained ammonium contains at least 40% platinum in the platinum regeneration step at least 93%.

Description

The invention relates to a process for the regeneration of platinum from PVC membranes of bipolar electrolysers for the production of peroxodisulfates or peroxodisulfuric acid.

In the electrode process, the platinum anode, depending on the current density, gradually dissolves and migrates to the cathode, the finely dispersed platinum particles being firmly entrapped by a PVC membrane adjacent to the carbon cathode in an amount of 0.33 to 0.51 g / piece. The recovery of platinum from these membranes has not yet been performed. The process of regenerating platinum from bipolar electrolysers described in GDR 115 097 (1974) only ensures the dissolution of platinum on the surface of corobone (substantially carbon) cathodes, since perfect elution of platinum from the entire membrane volume is not possible at low temperatures and low flow rates.

Up to 50% of platinum can be regenerated from PVC membranes under the conditions of platinum recovery mentioned in the above-cited patent. Another disadvantage of this process is the need for a large circulation apparatus for the circulation of a highly corrosive special bow (a mixture of hydrochloric acid, sulfuric acid, chlorine, hydrogen peroxide) and the need for additional electrolysers to obtain platinum from dilute solutions.

The procedures described in the literature for the recovery of platinum by ammonium chloroplatinate are based on the precipitation of concentrated chloroplatinic acid solutions (50-200 g platinum per liter) with a saturated ammonium chloride solution. Since only dilute solutions (1 to 2 g of platinum per liter) are produced in the elution of platinum by the royal bow from PVC membranes, it is necessary to concentrate them by evaporation. The concentration of undissolved lead salts and sulfuric acid, which is adsorbed to a considerable extent by the membrane, also increases. Applying the described methods of extractions based on concentrated solutions yields contaminated ammonium chloroplatinate at low yields.

These drawbacks are solved by an apparatus which is easy to use and maximally effective in regenerating the PVC membrane according to the invention. The method consists in treating the membranes coiled in a spiral for a maximum of three hours with a boiling royal bow, preferably with an elution module of 2.2 l / kg, in a glass vessel equipped with a reflux condenser. Elution with the royal bowel is preferably preceded by boiling the membranes with diluted nitric acid at a concentration of at least 10% by weight. Precipitation of ammonium chloroplatinate from acidic solutions with a maximum sulfuric acid content of 300 g / l and a platinum content of 5 to 10 g / l with solid ammonium chloride in an amount of 50 to 60 g / l in the presence of ethanol (minimum 30% by volume in the reaction mixture).

In order to maximize the degree of regeneration, the elution module (the ratio between the volume of the cell and the weight of the regenerated membranes) is decisive in addition to the temperature above 100 ° C, as shown in Table 1 and Figure 1, where the x-axis is plotted value of the elution module in 1 / kg and on the y-axis the value of the percentage of platinum regeneration.

Table 1

Elution module

(1 / kg) Degree regeneration 0.80 0.97 1.16 1.18 2.00 2.20 2.70 (%) 71.0 81.3 87.0 90.0 94.2 95.5 96.6 OF bigger of the stated data than 2.2 l / kg. it is obvious, that maximum eluce se reaches virtually eluting module To avoid change the elution module evaporator bows, need to be done regene ·

in a vessel equipped with a reflux condenser. The device for eluting the platinum from PVC membranes is shown in Fig. 2. The device consists of a glass vessel 5 immersed in one third of the oil bath 6. The vessel is provided with a reflux condenser 8.

Since the membranes contain a large amount of sulfuric acid and lead in addition to platinum, which hinder the recovery of platinum by ammonium chloride, it is necessary to boil the membranes before eluting with at least 10% by weight nitric acid.

Residues of a large platinum content of bowel are removed by boiling with water in an amount of at least 2.2 l / kg of membrane. The lentil elution is combined with the water stock and evaporated to a platinum content of 5 to 10 g / l. The sulfuric acid content shall not exceed 300 g / l. Precipitation with solid ammonium chloride is then carried out in the presence of at least 30% by volume of ethyl alcohol to eliminate ammonium chloroplatinate. The salt obtained is rinsed with ethyl alcohol at a concentration of at least 50% by volume and dried at 100 ° C in a hot-air oven.

Example

Four pieces of sorted 2,000 g PVC membranes containing 6 g of platinum are rolled up in a spiral and folded into a glass container 1. fitted with a reflux condenser cap 2. 4.4 liters of 10% by weight nitric acid are poured into the container. The vessel is placed in an oil bath 2 reaching one third of its height. The bath is heated to 105 ° C.

This arrangement results in an intensive circulation of the thermosiphon elution bath. Cooks (

up for one hour. This removes a substantial part of the sulfuric acid and lead from the membranes. The bath is aspirated by means of a water pump and the vessel is filled with 4.4 liters of royal meadows prepared from 35% by weight of hydrochloric acid and 65% by weight of nitric acid and by weight in a ratio of 3: 1 and extracted for three hours at boiling. The extract containing 4.45 g of platinum is aspirated into a collecting tank and the vessel is filled with 4.4 liters of warm water (preferably steam condensate) and avoided for one hour. Rinse water containing 1.20 g of platinum is aspirated into a common collection vessel.

The extract associated with the rinsing water is evaporated to one liter and, after cooling, filtered through a suitable acid-resistant filter material (eg polypropylene fiber non-woven cloth). This removes ballast dispersions of carbon, silicic acid, sulfate and lead chloride and thus avoids contamination of the final product. The sulfuric acid content after evaporation of the solution must not exceed 300 g / l. 50 g of ammonium chloride are added to the chloroplatinic acid solution thus prepared and after thorough washing, 500 ml of 96% ethyl alcohol are added. volume. The resulting ammonium chloroplatinate suspension is allowed to settle for 24 hours at temperatures minus 5 to 0 ° C. After decantation of the clear fraction, the precipitate was filtered through an acid-resistant filter. The precipitate is rinsed with 50% by volume ethyl alcohol cooled to 0 ° C. The aspirated salt is dried in a hot air oven at 100 ° C.

14.15 g of ammonium chloroplatinate having a platinum content of 40% by weight are obtained from the indicated number of membranes. The residue on the membrane is 0.2 g platinum, the mother liquor contains 0.1 g platinum per liter. The total degree of recovery of platinum is 93-95%.

Claims (2)

Method for the regeneration of platinum from PVC membranes of bipolar electrolysers for the production of peroxodisulphates or peroxodisulphuric acid, characterized in that the membranes coiled in a spiral are treated for at least three hours by boiling royal bow, preferably with an elution modulus of 2.2 l / kg in glass a flask equipped with a reflux condenser, whereupon the resulting acid solution having a maximum sulfuric acid content of 300 g / l and a platinum content of 5 to 10 g / l is precipitated with 50 to 60 g / l of solid ammonium chloroplatinate in the presence of ethyl alcohol added in such an amount; to form a solution having a concentration of at least 30% by volume. 2. A method according to claim 1, characterized in that the membranes are avoided with nitric acid, the concentration being at least 10% by volume being eluted by the royal bowel.