The conventional steps of mechanical methods include: metal disassembly, crushing, classification and subsequent treatment.
1.2 chemical method
1.2. 1 pyrometallurgy
There are mainly incineration melting method, high temperature oxidation method, smelting method, scum technology, electric arc furnace sintering method and so on.
1.2.2 wet recovery
Traditional hydrometallurgical techniques (such as leaching, solvent extraction, ion exchange, precipitation, reduction or electrodeposition, etc. ) and some new technologies (such as electrochemical technology and combined process). In recent years, cyanidation and solvent extraction are the main methods to extract precious metals in wet recovery technology.
Cyanidation (alkali leaching) is the direct leaching of specific metals in raw materials, that is, grinding electronic waste is soaked in sodium cyanide solution and air is introduced, and quicklime or sodium hydroxide is added to adjust the pH value, so that gold particles are dissolved in the solution. After the solution is separated, it is replaced by zinc wire.
Precipitate and pickling to obtain crude gold. The yield of cyanide gold extraction is as high as over 90%, with low cost and simple equipment. The disadvantage is that cyanide is toxic.
Solvent extraction is a common method to extract precious metals. Extraction generally includes extraction and back extraction. Study on extraction method
Usually, most of them focus on the selection of extractant and the optimization of extraction conditions. Commonly used extractants are: reported anion exchange extractant I.
It is pointed out that 99.06% copper sulfate crystals can be obtained by extracting copper from waste electronic circuit boards with an anion exchange extraction system containing triisooctyl amine (N235). Neutral phosphorus-containing extractant, such as tributyl phosphate (TBP), can be used to extract gold from cyanide solution.
Have a high gold carrying capacity. Neutral sulfur-containing extractant I (such as thioether RSR) is used to extract platinum group metals. Neutral oxygen-containing extractant:
If the secondary amine alcohol extractant N2 125 is used to extract gold from hydrochloric acid medium, the extraction rate of gold can reach 97.50%. Another example is extracting gold from precious metal solution containing gold, platinum and palladium with methyl isobutyl ketone (MIBK) extractant, and the extraction rate can reach above 99%. Chelating extractant: such as thienyl trifluoroacetylacetone (1-rA) and oxime extractant (LIX). The former has been successfully used to extract lanthanides and actinides from solid-liquid matrix.
It is made of metal. . ; It is reported that LIX79 is used to separate and extract Au(I) from the solution (NaCN = 1000 mg/L) containing Fe (II), Cu(I), Ni (II), Ag(I) and Zn (II), and the extraction rate can reach 90% ~ 95%. Organic carboxylic acids: such as sec-nonylphenoxyacetic acid developed in recent years. Cyclic ester phenolic acid extractant: especially suitable for extracting gold. The extraction rate of gold can reach 99% [1]. Amine extractant: It is reported that Ll, using quaternary ammonium salt extractant (ODMBAC) to extract Au (Ⅲ) from hydrochloric acid medium, the extraction rate is over 95%. Other extractants include xanthic acid extractant, macrocyclic polyether extractant and extractant for synergistic extraction.
2.2 Biological methods
Bacterial leaching of precious metals such as gold is a new method to extract precious metals from low-content materials, which was studied in 1980s.
2.3 liquid membrane extraction
The liquid membrane is composed of membrane solvent (the matrix material for membrane formation) and surfactant (the molecule contains hydrophilic groups and hydrophobic groups).
Materials), mobile carriers and internal phase reagents. Liquid membrane separation mechanism:
(1) Simple migration: the difference in solubility and diffusion coefficient of different components to be separated in the membrane leads to the speed of passing through the membrane.
Different implementations are separated,
(2) In-drop chemical reaction: A reagent which can react chemically with the solute is added to the receiving phase of the solute, so that the solute is dissolved in the membrane first.
In the solvent, it then diffuses to the surface of the membrane to react with the internal phase reagent. This reaction produces a new product, which cannot diffuse back through the membrane.
(3) Chemical reaction of membrane phase: a flowing carrier is added to the membrane phase, and the carrier molecules are first selected on the feed liquid (external phase) side of the liquid membrane.
It reacts chemically with a solute to generate an intermediate product, and then this intermediate product diffuses to the other side of the membrane, reacts with the internal phase reagent in the liquid membrane, releases the solute, and transfers the solute from the external phase to the internal phase.
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