NO884048L - ELECTROLYSE OF COPPER IN THIN SOLUTIONS CONTAINING LARGE AMOUNTS OF IRON. - Google Patents

Description

This invention includes a method for being able to electro-

lighter copper from thin water solutions containing larger amounts of iron, by introducing a medium to the electrolysis device during the electrolysis which precipitates the ferric (Fe+++) ions and renders them inert with regard to the electrolysis of copper itself. This preferably takes place at a pH value of 3-4 pH units.

It is known to those familiar with the electrolysis of valuable metals such as copper, nickel, cobalt, zinc and cadmium that so-called red/ox pairs, such as the pair Fe++/Fe+++ (f erro/ferri ) ions, lower the theoretical current yield with regard to the precious metal to be electrolysed, that the electrolysis itself first becomes unprofitable and then, with larger concentrations of Fe++/ Fe+++ ions in the solution, the entire deposition of the precious metal on the cathode fails.

Electrolysis in thin water solutions is well known. However, no one mentions the electrolysis of copper in thin water solutions containing larger amounts of iron, such as the waste water from copper mines, which is known to us.

We attempted electrolysis of thin copper solutions of only 200 mg/l copper which also contained 2300 mg/l iron. In normal electrolysis, where the current applied to the electrolysis device was only large enough to theoretically electrolyse the copper, this did not work at all. Absolutely no copper was deposited on the cathode.

However, to our great astonishment, by introducing a medium, here spoon sand (CaC03) or caustic soda (NaOH) to the solution inside the electrolysis device itself had a pH of between 3-4,

all the ferric (Fe+++) ions that otherwise interfered with the electrolysis of copper were precipitated as a hydroxide, and the electrolysis of copper proceeded as expected.

This by electrolysing the valuable metal from the water solution

and at the same time control the pH in the electrolyte to a value of

3-4 pH units by introducing a medium before or during the electrolysis which makes the ferric ions inert with respect to the precious metal electrolysis, is the very core of this invention.

It should be mentioned here that we have used calcium carbonate and caustic soda to precipitate the ferric ions as a hydroxide. Of course, it is also within this invention to use other media which raise the pH value to above the pH value for precipitation of ferric hydroxide in the electrolyte used. Mention may be made here of potassium hydroxide (KOH), metal carbonates, metal hydroxides such as, for example, hydroxides and carbonates of the precious metal to be electrolysed.

It is our feeling that this invention cannot only be applied

on thin mine waste water, but also of course on all thin solutions from which valuable metals are to be recovered and the iron is to be precipitated and removed as well.

The solution after the copper electrolysis contained some residues of

iron (Fe++ ions) and zinc. These metals were then completely removed by continuing the electrolysis with the introduction of calcium carbonate or caustic soda until the pH was between 6-7 units.

The filtrate from this step showed that the same technique as described above can also be used if all the metal ions in the electrolyte are to be removed.

The invention described above shall be described in more detail in the examples below.

Example 1

Mine waste water was electrolysed in an electrolysis device such as the one mentioned in Norwegian application no 87.2388.

Current = 13 amp, cell voltage = 6.3 volts, temperature = 20 °C. Liquid feeding = 12 litres/hour.

pH adjusted with shell sand (72% CaC03)

The example shows that with (here) addition of shell sand to the electrolysis unit to the outlet showed a pH of 3.56, copper was removed from this mine wastewater from 200 mg/l to 29 mg/l. The example also shows that without this pH adjustment it was

not possible to remove the copper.

Example 2

The object of this example was to prove that there is a pH niche between the pH values of about 3-4 where practically all ferric iron (Fe+++) is precipitated but that no copper is precipitated as Cu(0H)2, and that an electrolysis in this pH range is a real electrolysis of copper.

2 liters of a mine water was titrated with a 1 molar NaOH solution from a pH value of 1.95 up to a pH value of 5.08. Samples were taken at regular intervals and the filtrate analyzed for the metal concentrations at different pH values.

The example shows that at pH values > 4 copper probably precipitates as a Cu(0H)2 hydroxide and that at pH values

>5 Fe(0H)2 and Zn(0H)2 type hydroxides begin to precipitate.

This is familiar chemistry to those familiar with it.

Example 3

The object of this example was to show that if it is not of interest to take care of the copper separately, this technique also works if you want to remove all the elements with a higher pH value than 4.

A mine waste water was led into an electrolysis device such as the one mentioned in Norwegian application no 87.2388. The mine water was pumped in for about 1 hour without electricity applied, but with the pH regulated to about 5.5-5.8. This pH value is in practice just below the pH value that precipitates Fe(0H)2 and Zn(0H)2 hydroxides, but above the pH values that precipitate both Cu(0H)2 and Fe(0H)3 hydroxides.

The purpose was to show that by switching on the current, iron and partly zinc were precipitated, which would not otherwise have happened.

Shell sand (CaC03) used to adjust pH.

The example shows that the current creates ferric ions and that these precipitate when current is applied. Furthermore, if it is desired, all heavy metals as shown here can be removed, if it is a question of environmental protection.

Example 4

This example was carried out to further prove that all the heavy metals Cu,Fe,Zn could be removed from a thin solution, at a higher pH. NaOH is used here to adjust the pH. The example shows that by performing the electrolysis at a pH value of 6.20, the filtrate was practically free of the heavy metals copper, iron and zinc.

Claims (1)

Requirements 1 Procedure for electrolysis in thin water solutions containing copper, iron and zinc, as well as possibly other metals, characterized in that before or during the electrolysis, a medium is added which precipitates the iron as a hydroxide. Requirement 2 Procedure according to claim 1, characterized in that the medium added before or during the electrolysis is hydroxides or precursors thereof such as carbonates. Requirement 3 Procedure according to claim 1, characterized in that the degree of acidity in the water solution during the electrolysis is between a pH value of 3 and a pH value of 4 for the production of metallic copper on the cathode. Requirement 4 Procedure according to claim 1, characterized in that the degree of acidity in the water solution during electrolysis is greater than a pH value of 4 for complete removal of the metals copper, iron and zinc from the water solution.