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Method for purifying nickel and electrolyte to remove trace lead and zinc
In the nitriding of nickel sulfide, the traces of lead and zinc contained in the anode are also dissolved into the solution along with the nickel. For example, the gold-company measured, anode nickel sulfide-containing Pb0.03% ~ 0.05%, anolyte containing Pb4.5 ~ 8.0mg / L.
Nickel electrolysis removes trace lead and zinc by precipitation, ion exchange and solvent extraction.
1. Coprecipitation method for removing lead and zinc
During the precipitation process, some of the unsaturated components precipitate with the precipitate of the poorly soluble compound, a phenomenon known as "coprecipitation." The precipitation is divided into two types: adsorption coprecipitation and crystal coprecipitation. Crystallization coprecipitation is also called eutectic precipitation. In an electrolyte solution, when two substances can coexist with the electrolyte and their lattice structures are the same, they can form a precipitate having the same crystal structure and precipitate together from the solution under appropriate conditions. Called eutectic co-precipitation, the use of eutectic coprecipitation to remove impurities should consider the impact of the added reagent on the next process. In nickel- cobalt smelting, adsorption and precipitation are often used to remove impurities.
During the oxidation of chlorine gas and the release of cobalt from water, cobalt is oxidized, and lead and part of nickel are also oxidized to produce PbO 2 and Ni(OH) 3 and form a coprecipitation. This is because PbO 2 is removed by precipitation of Ni(OH) 3 precipitate. In addition, in the chlorine removal process of chlorine, the pH of the cobalt removal end point is increased, and zinc can also be removed from the human solution in a co-precipitation manner with nickel hydrate. The advantage of the coprecipitation process of removing lead and zinc is that it does not increase the process, and is completed in one process except lead, zinc, zinc removal and cobalt removal. The disadvantage is that the amount of slag is large and the slag contains nickel.
2. Ion exchange method The lead-zinc ion exchange method is one of methods for extracting metal from an electrolyte solution containing a valuable metal. During the contact of the feed liquid with the ion exchanger (solid matter), the ions on the ion exchanger adsorb ions of the same symbol (same) from the solution in the form of ion exchange. The ion-exchanged ion exchanger is washed with water and rinsed, and the ions to be extracted adsorbed on the ion exchanger are transferred into the eluent, and the ion exchanger is recycled for recycling.
There are some similarities between ion exchange and adsorption, but the difference is that ion exchange is stoichiometrically replaced, that is, the ion exchanger has an equal amount of ions of the same symbol for each changer with inorganic ions. Adsorption is only the absorption of solutes. The ion exchanger has two types of inorganic ion exchangers and ion exchange resins. Ion exchange resin is a synthetic three-dimensional crosslinked insoluble organic polymer with active genes. Generally, the polymer part, crosslinker and functional group are the main components that determine the chemical activity of the resin. It is composed of a fixed gene (such as -SO 3- , -COO -, etc.) and oppositely charged active ions (ie, exchangeable ions, also called counterions, such as H + ) . The fixed gene is firmly immobilized on the inert skeleton and cannot move. The living ions make the resin itself electrically neutral, and when the ion reaction occurs, the orientation can be moved.
Various ion exchange resins have a certain exchange capacity, so after a certain period of time, the resin is "saturated" and cannot be exchanged. At this time, the resin must be eluted "regenerated". The so-called regeneration is a temporary storage of ions that it adsorbs, and the resin returns to its original state and is returned for use. It is not difficult to see that the exchange resin reacts to the temporary storage of certain ions during the exchange process, and the resin itself does not change. [next]
The exchange capacity of ion exchange resins is an important property of ion exchange resins. It is determined by the number of functional groups introduced during the preparation of the resin. It is usually expressed in terms of the number of adsorbed ions exchanged per unit number (or unit volume) of resin.
The ion exchange process mainly consists of two stages, namely adsorption (or exchange) and desorption (elution regeneration).
(1) adsorption (exchange adsorption)
Adsorption is the main process of the ion exchange process. The raw liquid to be exchanged enters the exchange column at a certain flow rate, and ion exchange with the resin in the column is carried out through the exchanged solution from the outlet of the exchange column, and the outlet liquid is the exchanged solution. Should be sampled and analyzed regularly. When the ions to be exchanged in the outlet fluid reach saturation, the liquid is stopped and the resin is ready for elution regeneration.
The resin must be rinsed with water or other eluent prior to elution regeneration to remove the entrained solution between the resins in the column. The eluent can only rinse the residual solution of the resin clip in the column without eluting the metal ions that have been adsorbed by the resin. The eluent is generally made of clean water.
(2) elution regeneration
After the "saturated" resin is rinsed clean, a small amount of eluent is introduced from the time in the column, and the metal ions adsorbed by the resin exchange are eluted. After all the resin is regenerated, it is washed with pure water. The residual eluent between the resins in the column is removed, at which point the resin can be subjected to the next round of ion exchange.
The eluted metal is recovered or discarded according to the purpose of its exchange and the value of the metal.
The ion exchange method is a new slag-free process. It not only completely separates, purifies and collects metals, but also is easy to operate and easy to automate. It provides conditions for simplifying operation, improving working conditions and improving metal recovery rate. It is only suitable for treating dilute solutions with ion concentrations less than 10 -6 mol/L. When the metal ion concentration is greater than 1%, the separation effect is not good by this method.
In the high chloride solution, lead and zinc can combine with Cl - to form ZnCl 4 2- and PbCl 4 2- complex anions, while nickel does not form complex anions, and anion exchange resin can be used to remove impurities lead and zinc. In the production of nickel, some factories in China use ion exchange to remove lead and zinc, and use 701 resin to remove lead and 717 resin to remove zinc.
701 resin is a weakly basic anion exchange resin with a primary amine group RNH 3 + , Pb 2+ in a high Cl − solution, forming a PbCl 4 2- coupling anion, this complex anion and the 701 resin on the transition Anion Cl - exchange reaction:
2RNH 3 Cl+PbCl 4 2- =(RNH 3 )2PbCl 4 +2Cl -
Ni 2+ and Cl - do not form the conditions of PbCl 4 2- , and the lead adsorbed by the resin can be eluted to achieve the purpose of removing lead. The resin can be used after regeneration.
701 resin can also remove zinc, but the acidity is higher, and its zinc removal capacity is smaller than that of 717 resin.
717 resin is a strong basic anion exchange resin with quaternary amine group (-R 4 N) + , which can adsorb and exchange negatively charged ions in solution. Zn 2+ can easily form ZnCl 4 in high Cl - solution. The 2- anion anion, which is exchanged with the anion Cl- on the transformed 717 resin, is adsorbed on the resin, thereby reducing the zinc content in the solution, and backwashing the saturated resin with water or acid to achieve zinc removal. the goal of. The response is:
2R 4 NCl - +ZnCl 4 2- =(R 4 N) 2 ZnCl 4 +2Cl -
The resin adsorbing ZnCl 4 2- can be used continuously after being regenerated by water or dilute hydrochloric acid.
Ion exchange zinc degumming solution can reduce zinc to less than 0.3mg/L. The 717 anion exchange resin zinc removal process also has a certain effect on the removal of trace copper and lead in the solution.