CS264716B1 - Method of capturing rare metals from aqueous solutions of their salts - Google Patents

Abstract

The method deals with the capture of precious metals from their aqueous solutions. The essence is based on a precipitation reaction in the presence of water-soluble salts of dithiocarbamic acid in a weakly acidic pH range. The precious metals are removed in the form of an easily separable precipitate. The advantage of the proposed procedure is the possibility of removing precious metals from solutions containing a diverse mixture of organic substances.

Description

(57) The method deals with the capture of precious metals from their aqueous solutions. The essence is based on a precipitation reaction in the presence of water-soluble salts of dithiocarbamic acid in a weakly acidic pH range. Precious metals are being removed! in the form of a precipitated precipitate. The advantage of the proposed process is the possibility of removing noble metals from solutions containing a varied mixture of organic substances.

CS 264 716 Bl

The invention relates to a method for collecting noble metals from aqueous solutions of their salts.

Precious metals and their salts deposited on solid supports are often used as active ingredients in the realization of heterogeneous catalytic hydrogenation in chemical technology. During use, a portion of the active ingredient is released from the carrier and subsequently dissolved. In general, these solutions are complex systems containing organic and inorganic compounds of low relative molar mass as well as oligomeric organic compounds of varying composition and properties. The capture of precious metals from these solutions has economic reasons.

This problem is addressed in several ways. According to German Patent Specification DAS 1 926 042 the noble metals are separated electrochemically, which is disadvantageous in view of the energy consumption of the process and the disturbance of other compounds present in the system. The German patent DAS 1 964 922 recommends the separation of precious metals from aqueous solutions using anion exchangers. JP 70 27,321 discloses the separation of Pd from other metals (Cu, Fe, Ni) in two stages.

In the first one a strong basic anion exchanger is used and in the second a chelating ion exchanger. Gjerda et al., J. Chromatogr., 1980, 188 (2), 391 report separation of Pd, Pt and Hg by sorption on a strong base annexation and selective elution with various concentrated HCl solution.

Czechoslovak author certificate AO 222 920 discloses the separation of Pd from other metals using a strong basic anion exchange resin. A disadvantage of all ion exchange processes is the irreversible clogging of these substances by some organic substances which may be present in solution and the associated increased cost of regeneration and rapid degradation thereof. For these reasons, the use of ion exchangers for this purpose is limited.

The above-mentioned drawbacks are overcome by the present invention, which is based on the following: the pH of the solution containing the noble metal salt is adjusted to a value of 3 to 7. Any precipitated substances are removed from the solution. The water-soluble salt of dithiocarbamic acid at a concentration of 100-500 mg.l ^-1 is added in the next. Precious metal ions. they precipitate with the dithiocarbamic acid salt and thereby ensure the possibility of their separation from the solution. The recovery of the noble metals from the trapped precipitate is possible by known methods.

The advantage of the proposed process is its simplicity, low energy consumption, possibility of collecting precious metals also from solutions containing a varied mixture of organic compounds and low concentration of the noble metal salt.

Example 1

Waste water containing 40 ^gl-1 of organic matter, 6% NaOH and 2.1 mg · l ¹ in the form of an organic Pd was neutralized with HCl to pH 7. The precipitated organic sludge is filtered. Add 100 mg.l ^{-1 of the} diammonium salt of ethylenebisdithiocarbamic acid. After the precipitate formed on the filter paper, the residual concentration of Pd in the solution was 0.21 mg.l ¹ .

EXAMPLE 2 The pH of the waste water composition as in Example 1 is adjusted to 3. After removal of the precipitated sludge, 500 mg.l ^{-1 of the} dipotassium salt of ethylenebisdithiocarbamic acid is added. After collecting the precipitate formed by filtration, the residual concentration of Pd in the solution is 0.07 mg.l ^-1 .

Example 3

Waste water containing 400 mg.l ^-1 toluene, 4000 mg.l ^-1 methanol, 15% by weight Naci, 200 mg.l ^-1 4-nitrosodiphenylamine, 150 mg.l ^-1 4-aminodiphenylamine, 30 gl ^-1 other organic and 3.02 mg.l ^-1 Pd whose pH = 10 is neutralized with H ₂ SO ₄ to pH = 5. After removal of the precipitated sludge, 225 mg.l ^-1 sodium dimethyldithiocarbamate is added. After filtering off the precipitate formed, the residual concentration of Pd in the solution is 0.52 mg.l ¹ .

Claims (1)

OBJECT OF THE INVENTION SpĎsob collecting precious metals from aqueous solutions of their salts, characterized in that the pH of the treated solution was adjusted to 3-7, is added 100 to 500 mg.l ^one water-soluble salt of dithiocarbamic acid, and the precious metals are collected as a precipitate.