Study on Direct Chlorination Leaching Process of Rich Platinum Nickel Copper

Falconbridge (of Falconbridge) Nickel Refinery Norway reduction treatment of the noble metal containing 0.002% of the total of nickel matte converter, nickel matte is first milled, and then concentrated hydrochloric selective leaching of nickel, copper sulfide and precious metals remain in the leaching residue . The leaching residue is subjected to solvent extraction to remove impurities to produce crystalline nickel chloride, which is then converted into granular nickel oxide in a boiling reactor, and then reduced with hydrogen in a rotary kiln to produce commercial nickel containing 98% nickel. After the leaching slag is calcined to remove sulfur, the copper is leached with a waste copper electrolyte. The precious metal is recovered from the copper leaching residue.

When treated by this method the plant rich in platinum group metals from South Africa (1 ~ 2kg / t) nickel matte, the noble metal found greater losses during the firing, the leaching step, a serious economic impact. Therefore, the leaching slag after leaching nickel with concentrated hydrochloric acid is leached out of the pot by aqueous solution chlorination, and the precious metal concentrate having a weight of 1% of nickel ice copper is not produced.

1. Liquid chlorination leaching of platinum-rich nickel-copper and high-ice nickel

In the leaching residue of the platinum-rich nickel-copper copper leached with concentrated hydrochloric acid to remove nickel, copper is mainly present in the form of copper sulfide. The liquid chlorination method leaches copper sulfide, which is copper-containing. Chlorine gas is introduced into the mixed slurry of nickel hydrochloric acid solution and copper sulfide leaching residue. In order to prevent the precipitation of cuprous chloride during the leaching process, the leachate must contain a chloride such as nickel chloride or free hydrochloric acid. At this point, the chlorination of copper is:

2Cu++Cl ₂ 2Cu ₂ ⁺ +2Cl ^- (1)

Cu ₂ S+Cu ₂ ⁺ CuS+2Cu ⁺ (2)

CuS+Cu ₂ ⁺ 2Cu ₂ ⁺ +S (3)

S+2e S ₂ ^- (4)

Cu ₂ ⁺ +S ₂ ^- CuS (5)

The complete leaching of copper depends on the reaction formula (3). The reaction formulas (4) and (5) only indicate whether copper is precipitated as sulfide or by adjusting the redox potential of the leaching process (measured by platinum and saturated calomel electrode insertion solution) to bring copper into solution? That is, at a high oxidation-reduction potential, the reaction proceeds according to the formula (3); and at a low oxidation-reduction potential and a specific temperature, acidity, and copper concentration, the progress of the reaction formulas (4) and (5) is accelerated. A large amount of sulfur ions and sulfides are generated. When the concentration of copper sulfide exceeds its solubility product, a copper sulfide precipitate is formed, at which time the copper cannot be completely leached.

The minimum redox potential necessary for copper to leach as completely as possible depends primarily on the copper concentration, acidity and temperature in the solution. However, in practice, the potential range of the leaching operation (Fig. 1) is between 0.35 and 0.45V. The oxidized leaching rate of copper is highest in this potential range, and the precious metal is substantially insoluble. This may be because the precious metal does not dissolve in this potential interval, or may react with copper. After dissolution, the reaction is re-formed by the reaction of (6) and (7):

S+2e S ^2- (6)

P ³⁺ +S ^2- PS (7)

Figure 1 Dissolution rate of different potentials

During the leaching process, all free selenium will react with precious metal ions (possibly like formulas (6) and (7)) to form insoluble selenide precipitates.

In order to increase the leaching rate of copper and to prevent precious metals from entering the solution as much as possible, a suitable redox potential can be selected from the curve of Fig. 1 in advance. It should be noted, however, that the dissolution profiles of copper and precious metals in the graph are affected by changes in copper concentration, acidity, and temperature in the solution. When operating at high acid, low copper concentrations and high temperature operating conditions, the curve shifts slightly to the left; at low acidity and high copper concentration and low temperature operating conditions, the curve shifts slightly to the right.

The process of leaching platinum-rich nickel-copper copper by aqueous solution chlorination is also suitable for treating the original high-ice nickel containing the precious metal, sulfur and selenium in the plant. When the high ice nickel leaching slag composed of the above composition is leached at the selected oxidation-reduction potential, the leaching slag is leached by tetrachloroethylene to remove sulfur, and the content of the precious metal in the concentrate is 100 times higher than that of the high ice nickel. Therefore, the method can treat both the platinum-rich nickel matte and the high-ice nickel to recover the precious metal concentrate. This will reduce the factory's delivery of intermediate ice high nickel to the Eagle Bridge plant and take advantage of the nickel refining capabilities of the Norwegian plant.

Second, the process of chlorination of platinized nickel-copper solution

The process and product of the Norwegian nickel refinery, which has been improved to process South Africa's rich platinum nickel coil (and converter high ice nickel) is as follows.

(1) Concentrated hydrochloric acid leaching nickel. After the nickel ice copper is ground, it is leached in a rubber lining stirred leaching tank. Nickel enters the solution in the form of nickel chloride, and copper sulfide and precious metals remain in the leach residue. After the nickel chloride solution is purified by extraction to remove impurities, it is made into crystalline nickel chloride, and converted into granular nickel oxide in a boiling reactor, and then reduced by hydrogen in a rotary kiln to produce a commercial nickel having a purity of 98%.

(2) Removal of copper from nickel leaching residue. The slag after leaching nickel mainly contains copper sulfide. It is chlorinated in a nickel chloride or hydrochloric acid solution, and sulfur and precious metals are left in the leaching residue. The leaching removal copper is also a rubber-lined agitated leaching tank. The leaching tank is equipped with two sets of independent platinum-saturated calomel electrodes, and the measured data is sent to an electronic computer for processing. One set of electrodes is used to measure the redox potential of the leaching process to control the supply of chlorine gas; the other set is used to signal the alarm when the pre-adjusted redox potential range is too high or too low, and can be read at any time. Or lower than the value of the preset potential to ensure operation within the selected range of redox potential. The use of such a device is mainly to ensure that the supplied chlorine gas is not excessive, so as to prevent the dissolution of the precious metal due to an increase in the oxidation-reduction potential, or the incomplete dissolution of the copper due to the low potential. After the copper is terminated, it is subjected to pressure filtration through a propylene glycol plate and frame filter press to produce a sulfur-containing precious metal concentrate. Hydrogen sulfide is introduced into the filtered copper chloride solution to form copper sulfide precipitated by copper, and is sent to a copper system for treatment.

(3) Desulfurization of copper concentrates. The filter cake of the pressure filter is successively supplied into the glass-lined stirring tank indirectly heated by the jacket through a feeding tank equipped with a weighing sensor, and the hot chlorobenzene is added to dissolve the sulfur, and the slurry after dissolving the sulfur is centrifuged by stainless steel. The pump is continuously pumped to a steam jacket heated sealed filter press to filter out the precious metal concentrate. After the filtrate precipitates sulfur crystals, the sulfur is dehydrated by a centrifuge to recover sulfur. The tetrachloroethylene solution is returned to the next desulfurization by regeneration.

(4) Enrichment of precious metal concentrates. The desulfurized concentrate is subjected to sulphation roasting in a small calciner. Roasting is to place the concentrate in a steel pan in the furnace and adjust the air into the furnace to control the firing rate. In order to prevent the air from entering the furnace too fast and causing the loss of the roasted dust particles, the firing rate should not be too fast. The furnace temperature is controlled at about 500 °C. The calcined sand is leached by dilute sulfuric acid to remove heavy metal sulfate, filtered, washed, dried, mixed and discharged in a "V" type rotary mixer (capacity 1000 kg), weighed and automatically sampled for testing. The final precious metal concentrate grade produced in practice depends to a large extent on the precious metal content and insoluble components of the nickel matte material. Among the insoluble components, the content of silicon is the most affected. Under normal circumstances, when processing nickel beryllium copper raw materials containing 0.07% to 0.08% of lead , the produced precious metal concentrate contains 15% to 30% of platinum and a considerable amount of other precious metals.

Since the production process is continuous, it is difficult to accurately determine the weight and grade of a batch of raw materials and concentrates. Tables 1 and 2 list the analytical data obtained from the laboratory batch processing of platinum-rich nickel matte, which does not include losses in transportation and soot during the production process. It can be seen from the table that in this process, various precious metals are concentrated more than 330 times in the concentrate, and the recovery rates are all greater than 92%. The final concentrate yield is less than 1%.

Table 1 Grades of nickel ice copper and concentrate and precious metal enrichment rate

Table 2 Metal balance of raw materials and products

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