Comprehensive recovery process of valuable metals in tungsten slag
Characteristics of tungsten having a plurality of metal deposits symbiosis, tungsten smelting alkali leaching process to the main current, almost all tungsten alkali leaching residues (hereinafter referred to as tungsten slag) all contain a small amount of Ta, Nb, Sc and other valuable metals, domestic tungsten slag Ta 2 O 5 + Nb 2 O 5 total content (mass fraction) of 0.54% to 0.65%, while tantalum and niobium ore of tantalum and niobium oxide content of 0.02% or more will have industrial exploitation value; simultaneously, The WO 3 content in the tungsten slag is 4% to 7%, and the Sc 2 O 3 content is 0.02% to 0.04%, which also has a large comprehensive recovery value. However, at present, the recovery of tungsten slag in China's tungsten smelting plant basically remains at the stage of simple recovery of tungsten and partial recovery of ruthenium , but no recovery of ruthenium. The survey results show that the tungsten slag produced by China's tungsten smelter in the past 20 years has reached more than 600,000 tons. The storage of tungsten slag has made the valuable metal resources not fully utilized and polluted the environment. Therefore, with the continuous consumption of mineral resources and the increasing demand for these metals, it is necessary to comprehensively recover valuable metals in tungsten slag. Here, the authors studied the recovery process of W, Ta, Nb and Sc in tungsten slag.
First, the experimental method
(1) Experimental materials
The experimental tungsten slag sample is supplied by a domestic tungsten smelting plant, and the tungsten slag with a particle size of less than 180 μm accounts for more than 95%. The chemical composition is shown in Table 1.
Table 1 Elemental analysis of tungsten slag w∕%
(two) process
The process flow used in the experiment is shown in Figure 1.
Figure 1 Flow chart of the recovery process of thorium in slag
(3) Experimental analysis methods
The content of tungsten was analyzed by spectrophotometry during the experiment, and the content of strontium and barium was analyzed by X-ray fluorescence analysis.
(4) Basic principles of the process
1. Roasting water immersion process
The tungsten slag contains a large amount of iron , manganese and a small amount of tungsten, tin , antimony, bismuth, antimony and the like. When baking soda, sodium tartrate, sodium silicate and sodium citrate and sodium citrate which are insoluble in water are formed. After leaching by water leaching, strontium, barium and tungsten, silicon are initially separated, and tungsten is sodium tungstate. The form enters the solution, and the ruthenium and osmium enter the slag in the form of sodium citrate and sodium citrate. However, during the flooding process, only part of the sodium silicate enters the solution, and the rest remains in the water leaching residue.
2, dilute acid desiliconization
If the water leaching residue is directly leached by high acid, silica gel is likely to occur, and the impurity leaching rate and the filtration performance of the leaching slag are reduced. Since silicic acid can form a sol under certain conditions, the solute in the sol can pass through ordinary filter paper and filter cloth, and it is easy to be polymerized and precipitated when changing conditions (such as temperature, acidity, time, etc.), therefore, it can be diluted at low temperature. The acid is rapidly processed and filtered prior to polymerization of the silicic acid to remove most of the silicon.
3, high acid leaching
The dilute acid desiliconization slag removes some iron, manganese, calcium and other impurities, but most of the impurities remain in the slag and can be removed by high acid leaching. In the case of high acid leaching, sodium citrate and sodium citrate are converted into tannic acid and citric acid with low solubility, most of which remain in the slag, and most of the impurities such as iron, manganese, calcium, etc. are leached into the solution to reach 钽铌The purpose of enrichment. The main reactions of high acid leaching are as follows:
NaTaO 3 + HCl = HTaO 3 + NaCl,
NaNbO 3 + HCl = HNbO 3 + NaCl.
In the case of high acid leaching, the greater the acidity, the higher the leaching rate of impurities and the greater the loss of hydrazine.
Second, the experimental results and discussion
(1) Soda roasting and flooding
The effects of soda dosage, calcination temperature, calcination time, water immersion liquid-solid ratio, water immersion time and water immersion temperature on the leaching rate of tungsten were investigated by orthogonal experiment. The results show that the influence of the first three factors on the leaching rate of tungsten decreases in turn, and the influence of the latter three factors is not significant. The effect of soda dosage n, calcination temperature T and calcination time t on tungsten leaching rate is shown in Figures 2 to 4.
Based on the influence of various factors, the best conditions for determining this process are:
a. The amount of soda is 6.0 times the theoretical amount;
b. calcination temperature: 850 ~ 950 ° C;
c. roasting time: 50 min;
d. water immersion liquid to solid ratio: 6:1;
e. Water immersion time: 90min;
f. Water immersion temperature: 95 to 100 °C.
The verification experiment was carried out under the above optimal conditions, and the results showed that the leaching rate of tungsten was up to 80%. In general, the tungsten leaching rate is not high, mainly due to the presence of CaO or CaCO 3 in the tungsten slag, and WO 4 2 - and CaO entering the leaching solution to form white tungsten .
Fig. 2 Effect of soda dosage n on W leaching rate η
Fig. 3 Effect of calcination temperature T on W leaching rate η
Fig. 4 Effect of calcination time t on W leaching rate η
(two) dilute acid desiliconization
The water leaching residue is vigorously leached in dilute hydrochloric acid with a volume fraction of 7% to 9% for 1 to 2 minutes, and is quickly filtered and washed. The desiliconization rate of the process can reach 60%. The experimental results show that silica gel is easily formed when the concentration of hydrochloric acid is too high, which not only has poor silicon removal effect, but also is difficult to filter; and too long reaction time or slow filtration rate is easy to cause sol polymerization. Therefore, the operating conditions of dilute acid desiliconization should be strictly controlled.
(3) High acid leaching
The effects of hydrochloric acid concentration, leaching solution solid ratio, leaching temperature T and leaching time t on strontium recovery rate and strontium content in enriched slag were investigated by orthogonal experiment. The results are shown in Figures 5-8. Among them, w(C) is the recovery rate of 钽 and 铌.
According to the experimental results, the best conditions for high acid leaching are:
a. hydrochloric acid concentration: 20%;
b. Leachate solid ratio: 6:1;
c. leaching time: 60min;
d. Leaching temperature: 95 to 100 °C.
1-w(Ta 2 O 5 +Nb 2 O 5 )-w(HCl) curve;
2-w(C)-w(HCl) curve
Figure 5 Effect of hydrochloric acid concentration on cesium enrichment
1-w(Ta 2 O 5 +Nb 2 O 5 )-w(HCl) curve;
2-w(C)-w(HCl) curve
Figure 6 Effect of acid immersion liquid to solid ratio on enthalpy enrichment
1-w(Ta 2 O 5 +Nb 2 O 5 )-w(HCl) curve;
2-w(C)-w(HCl) curve
Figure 7 Effect of acid leaching temperature T on enthalpy enrichment
1-w(Ta 2 O 5 +Nb 2 O 5 )-w(HCl) curve;
2-w(C)-w(HCl) curve
Figure 8 Effect of acid leaching time t on enthalpy enrichment
According to the above optimal conditions, the verification experiment was carried out to obtain the typical composition of the slag-rich slag, as shown in Table 2.
Table 2 slag-rich slag composition and metal recovery rate w∕%
According to the current industrial production practice, the material containing Ta 2 O 5 in 3% or more can be extracted by slurry. Therefore, the slag-rich slag obtained from the test can be directly processed into the existing hydrazine production process to finally obtain potassium fluoroantimonate and bismuth pentoxide products. The waste acid solution obtained after high acid leaching can be returned to the dilute acid desiliconization process, and the ruthenium is mainly concentrated in the desiliconization waste liquid and the high acid leaching liquid, and can be extracted by solvent extraction, ion exchange or chemical precipitation.
Third, the conclusion
(1) The process can treat tungsten slag containing 0.15% Ta 2 O 5 and 0.46% Nb 2 O 5 , and obtain cerium-rich slag with an average content of 4.06% of Ta 2 O 5 and 11.83% of Nb 2 O 5 The metal recovery rate is 79.46%, and the enriched slag can be directly used for industrial production.
(2) The experiment determined the optimum process conditions for comprehensive recovery of valuable metals ruthenium and osmium from tungsten slag; that is, the amount of soda used was 6.0 times the theoretical amount, the calcination temperature was 850-950 ° C, the calcination time was 50 min, and water immersion The liquid to solid ratio is 6:1.
(3) The process flow is relatively simple, and the raw materials used are cheap and easy to obtain, and the production cost is low.
(4) Tungsten can be recovered by ion exchange in an aqueous immersion liquid, and hydrazine can be recovered by extraction in a hydrochloric acid leaching solution.
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