Resin regeneration technology

January 31, 2024

The saturated resin discharged from the adsorption section, because almost all of the resin reactive groups are occupied by gold , silver anion and other impurity metals in the slurry, such as copper , zinc cyanide anion and free cyanide CN-, Therefore, this saturated gold-loaded resin is no longer adsorbed. The purpose of reclaiming the saturated resin is to desorb the gold and silver into the precious liquid as completely as possible from the resin, and obtain a pure, high-grade noble liquid, so as to reduce the burden of work and production when extracting gold from the precious liquid in the next step. The finished product with higher purity is obtained; in addition, the impurity metal adsorbed on the resin is removed to the utmost, so that the adsorption activity of the resin is restored, so that the resin is repeatedly used.
Table 1 lists the content (mg/g) of each component in the AM-2Б anion exchange resin before and after regeneration.

Table 1 AM-2Б anion exchange resin component content before and after regeneration w/ ( m g· g ^-1 )
metal element	Au	Ag	Zn	Co	Fe	Ni	Cu	C N ^-	Cl ^-	OH ^-
Saturated resin	15.2	21.3	8	4.1	2.8	1.6	0.95	twenty two	7.4	13.4
Recycled resin	0.3	0.5	0.6	0.1	0.9	0.6	0.8	0.5	2.5	46

The above data indicates that the resin composition differs greatly before and after regeneration. The saturated resin contains no more than 20% of the total amount of metals and impurities (excluding CN ^- , Cl ^- , OH ^- ions). These metal impurities directly affect the choice of resin regeneration process. The amount of gold, silver and impurities remaining on the resin after regeneration is only 5% to 6% of the total adsorption capacity of the saturated resin. That is to say, the resin is regenerated to remove 94% to 95% of gold and impurities, and the resin is basically recovered. Adsorption performance.
1. The basic principle of resin regeneration
The basic method of regenerating a saturated resin is desorption (or elution), which is a process of precipitating the adsorbed ions into a solution. The original solution through the resin in this process is called desorbent, and the solution containing ions recovered from the resin is called eluate (or regenerant). The regeneration of the resin is achieved by desorbing the bottom up through a desorption column equipped with an ion exchange resin. The ions in the desorbed solution desorb the ions A adsorbed by the resin by the following ion exchange reaction: [next]

When desorbing the resin with several times the resin volume of the desorbent, the first few eluates do not contain A ions, because the resin is not saturated with the B ions in the desorbent, only when the desorption process proceeds to After several parts of the desorbent, the resin no longer absorbs the ion B. It is only beginning to strongly desorb ion A, at which point the concentration of ion A in the eluate discharged from the column will gradually increase until the concentration of A in the eluate reaches a maximum. Thereafter, continue to pass the desorption solution into the column, because the A content in the resin has gradually decreased and is saturated with the ion B, so the desorption exchange reaction zone from the bottom to the top along the desorption column is gradually reduced, resulting in subsequent desorption column The concentration of ion A in the ejected eluate begins to decrease again. [next]
In production practice, it is necessary to determine the volume of desorbent required to achieve the highest concentration of ion A in the eluate and determine the total volume of desorbent required to completely desorb ion A. The desorption characteristics of the anion exchange resin AM-2Б and factory practice confirmed that to completely desorb gold from the resin, the volume of the desorbent should be more than 20 times the volume of the resin, using 9 parts of the resin volume of the desorbent, the resin is gold The desorption rate can reach 97%, that is, about 97% of the gold on the resin can be recovered. Therefore, in order to reduce the amount of gold in as little as possible in the eluate, the eluate (precious liquid) with the highest gold concentration is obtained, so as to reduce the difficulty in handling gold and the disposal cost from the precious liquid. Usually, the eluate is divided into several parts, 9 parts of the eluate is sent to recover the gold, and the 10th part of the eluate containing less gold is returned to the desorption operation as a desorption liquid.
In production, the eluate containing heavy metal impurities obtained by resin regeneration is generally not treated because it is not economically economical. The temperature rise is important for reducing the width of the desorption zone and accelerating the regeneration process. In fact, the regeneration treatment of the resin AM~2Б is carried out at 50~60 °C. Too high a temperature will destroy the thermal stability of the resin.
2. Process of resin regeneration
The figure below shows the regeneration process of AM-2Б anion exchange resin from a gold extraction plant in the former Soviet Union. The entire process is divided into 8 processes.

1) The washing mud resin contains slime and wood chips, which will absorb the solvent and contaminate the solution of other processes. Therefore, fresh water should be supplied from the bottom to the top in the regeneration column for 3~4 hours, and the resin of each volume should be consumed 2 ~3 volumes of fresh water. When processing the slurry of the flotation concentrate, the resin is preferably washed with hot water to sufficiently wash away the flotation agent adsorbed on the surface of the resin. The washing water after washing the mud returns to the cyanidation process. The quality of the washing mud was identified by visually observing the content of suspended solids in the washing water.
2) Cyanidation treatment After the resin is washed, it is treated with 4%~5% NaCN solution to remove the cyanide complex of iron and copper in the resin. The exchange reaction of CN-ion substituted copper and iron complex ions is:

[next]

After this method is treated with 5 times the resin volume of the desorbent for 30~36h, only 80% copper and 50%~60% iron are removed from the resin, and 15% gold and 40% in the process~ 50% of the silver is washed out, and the cyanidation treatment is more toxic, so now only cyanide treatment is carried out when iron and copper in the resin accumulate to seriously reduce the operating capacity of the resin to gold.
3) Washing cyanide After cyanidation, the residual cyanide solution in the gap of the resin particles accounts for about 50% of the total volume of the regenerated column. Wash with 5 times the resin volume of water for 15~18h to wash away the residual cyanide solution and the cyanide ion CN ^- adsorbed on the surface of the resin. The wash water is returned for use in the preparation of the cyanide solution.
4) Acid treatment After the resin was washed to remove cyanide, zinc and a part of the drill in the resin were dissolved by using a 3% sulfuric acid solution, and cyanide and CN- were volatilized and removed. Its chemical reaction is as follows:

The acid treatment time is 30~36h, and a volume of resin will consume 6 volumes of acid solution. The discharged washing liquid is neutralized in the storage tank with lye and then pumped into the tailings storage.
5) Thiourea desorbing gold Compared with acetone, methanol and ethanol, acid thiourea solution is the most effective desorbent for gold and silver. Because thiourea reacts with gold to form a complex cation [AuSC(NH ₂ ) ₂ ] ²⁺ , this complex cation cannot be adsorbed by the anion exchange resin and enters the solution. When the AM-2b gold-loaded resin was desorbed by the acidic thiourea solution, it was found that the head 1.5~2.0 volume of the eluate contained almost no gold and no thiourea. In order to prevent the precious liquid discharged after dilution, the desorption of gold was recovered. The operation is divided into two steps: 1 adsorption of thiourea; 2 desorption of gold. Adsorption of thiourea is prepared to desorb gold to ensure a high concentration of eluate.
The adsorption of thiourea is carried out by using thiourea and 3% sulfuric acid solution with a mass fraction of 9% to 1.5 times the resin volume to treat the resin for 30 to 36 hours. In the production practice, the gold-depleted liquid discharged from this process is used as a desorbing liquid to produce a high-gold-containing noble liquid in the next desorption step.
Desorption gold is the main process in the resin regeneration process and a key step in recovering gold from the resin. The working time of desorbing gold is as long as 75~90h. This is because the desorption rate of gold is small, the affinity of the resin to the gold cyanide ion is the largest, and the gold is concentrated in the minimum volume of the eluate. The optimum composition of the desorbent is 8% to 9% thiourea and 2.5% to 3.0% sulfuric acid.
At the time of desorption, the exchange reaction is carried out by sulfate ions, first destroying the gold cyanide complex in the resin, and then generating a positively charged thiourea gold ion, and transferring the solution from the resin phase. The desorption of thiourea is that it forms a stable complex cation with gold and silver [AuSC(NH ₂ ) ₂ ] ⁺ into aqueous solution: [next]

At the same time, volatile hydrogen cyanide gas is also precipitated. Since the desorption process is only the exchange of sulfate ions. Therefore, the consumption of thiourea is not large, and it is limited to mechanical losses and side reactions. After desorption, the resin was completely converted to sulfate ion SO ₄ ² -type.
The desorption of gold is generally carried out countercurrently in several columns in series, which ensures the production of gold-containing eluates and a high gold desorption rate.
6) Washing the thiourea After desorbing the gold, the thiourea remains in the gap between the surface and the resin particles, and these thioureas must be returned to the desorption process. To this end, 1 volume of resin was washed with 3 volumes of water. The thiourea should be washed to remove the thiourea. First, the thiourea should be recovered. Second, if this part of thiourea is brought back to the adsorption process, it will form a poorly soluble sulfide precipitate in the resin phase to lower the resin. Exchange capacity.
7) Alkali treatment The purpose of the alkali treatment is to remove insoluble matter such as silicate in the resin, and to convert the resin from SO ₄ ^2- type to OH ^- form. The alkali treatment is usually carried out using a 3% to 4% sodium hydroxide solution, and the lye consumption is 4 to 5 times the resin volume. The effluent of this process is used to neutralize the resin acid treated solution.
8) Washing and removing alkali The excess and residual alkali in the resin are washed away with water, and the washing water is drained for preparation of fresh alkali liquor.
3. Regeneration characteristics of saturated silver resin
In the above operation of adsorbing and recovering silver from the silver-containing cyanide slurry by the two-stage cyanidation-adsorption process, two kinds of saturated resins are produced: 1 resin containing about gold and silver; 2 mainly silver-saturated resin. The regeneration treatment of these two resins has its own characteristics, which is caused by the mobility and desorption rate of silver ions in the resin.
During the regeneration process, when acid treatment is carried out with a sulfuric acid solution of 6 times the resin volume, in addition to zinc and nickel being washed out, 35% to 40% of silver is transferred into the solution in the form of AgCN colloid. Therefore, when the content of zinc and nickel in the resin is not high, in order to leave the silver on the resin, it is sufficient to perform acid treatment using only an acid solution of 2 to 3 times the volume of the resin.
Since the desorption rate of silver is faster than that of gold, the amount of silver in the eluate has reached a maximum when passing through a thiourea desorbent of 1.5 times the volume of the resin. Therefore, when the amount of thiourea added is not large, and the resin is still adsorbing thiourea, the silver is rapidly desorbed from the resin, and the average volume mass of silver in the eluate is more than 1000 mg/L. Therefore, the eluate can be sent to electrolytic silver extraction.
Using a desorption solution with a volume of 3.5 to 4 times the resin volume of 3% thiourea and 2% sulfuric acid, much less than the gold desorption liquid (mass fraction 8% to 9%), and the amount of desorbed liquid is only equivalent to five of the desorption gold. One of the parts, resulting in a significant reduction in thiourea consumption. [next]
Since the silver desorption rate is fast, the flow rate of the desorbent in the regeneration column can reach 3 times the desorption liquid of the resin volume per hour, which greatly accelerates the regeneration process.
Table 2 lists the metal content (mg/g) before and after regeneration of the resin product in the two-stage cyanidation-adsorption process and regeneration process. The data in the table shows that after acid treatment of the saturated resin, zinc and nickel are fully desorbed, and 30% to 40% of copper and iron are desorbed. The desorption rate of silver is higher than that of gold in the first stage saturated resin, and the residual amount of silver in the resin after regeneration is only 1/3 of gold.

Table 2 Metal content of resin products in two-stage cyanidation - adsorption and regeneration process w/ ( m g· g ^-1 )
metal	Au		Ag		Cu		Fe		Zn		Ni
Resin	I	II	I	II	I	II	I	II	I	II	I	II
Saturated resin	24.4	0.75	18.3	26.4	0.64	2.9	0.77	8.63	7.69	0.21	1.37	0.21
Acid treated resin	twenty four	0.78	14.1	20.8	0.32	1.81	0.62	5.8	0.14	0.09	0.12	0.1
Recycled resin	0.62	0.09	0.22	0.08	0.06	Trace amount	0.49	1	0.04	0.05	0.07	0.09

4. Resin regeneration operation mode
The operation of the resin in the regeneration column can be divided into three types: discontinuous, semi-continuous and continuous.
Intermittent regeneration of the resin is carried out in one or several regeneration columns. It does not require many columns and corresponding work sites, but the quality of the recycled resin produced is not high and is only used in small-scale regeneration operations.
The semi-continuous regeneration method is a method of regenerating resin commonly used in existing adsorption plants in the Soviet Union. It is carried out in a series of regenerative columns, each of which performs only one specific job. The resin is supplied to the column at regular intervals, and the solution is continuously supplied to the column. This method has a high metal recovery rate and can produce a noble liquid with a high gold content.
Continuous regeneration is the continuous reverse desorption of the resin and the desorbent in a series of specially designed regeneration columns. The process can be automated, so the desorption efficiency of the resin is high. However, since continuous reverse flow of the resin and the solution cannot be caused in the solid resin column, a special structure of the regeneration column is required to achieve continuous regeneration.
The point of resin regeneration is that the desorbed liquid is supplied to the column at a predetermined speed, and the resin is strictly transferred along the respective columns in a certain volume. Only by this operation can the required eluate and resin volume ratio be achieved. For the desorption of gold, if the volume of the resin transferred per batch is specified to be 300 L, the regeneration column is required to pass 1500-1600 L of thiourea desorbed solution during this period, and the same volume of eluate is produced.

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