Study on Extraction of Valence Components from Iron Strontium, Lead and Silver Mixed Slag

Yang Yuexin

Abstract : In order to recover the valuable components in the mixed slags of iron slag and lead and silver formed during the “precocious” smelting of zinc smelting, this study adopts the roasting pretreatment-sulfuric acid leaching process to enrich the mixed slag at 500°C~600°C. After roasting the mixed slag for 1~1.5h, the roasted slag is leached at a temperature of 90°C~95°C, a liquid/solid ratio of 1~1.5:1, and a concentrated sulfuric acid dosage of 35~40mL/100g slag (close to the theoretical acid consumption). 1.5~2h, at the end of leaching, adding 0.5% NaCl, leaching zinc and iron in the slag by about 95%, the slag rate is less than 13%, the lead-silver enrichment multiple is more than 8 times, sometimes even more than 10 times. The content of lead in the enriched slag is up to 30%, and silver is up to 3kg/t. It can be used as a lead-added raw material.

Key words: iron slag, lead silver slag, roasting, acid leaching

1 Introduction

In the process of hydrometallurgical zinc smelting, in order to reduce the iron pressure during the iron removal process when high iron iron zinc concentrates are processed, zinc oxide baking sand is often added at the end of the acid leaching to reduce the acidity of the leaching solution, and some iron iron slags are started before the acid concentration. The form of precipitation, industrially known as "premature", "premature" to a large extent reduced the iron content of the acid leaching supernatant, it also reduces the iron removal pressure [1]. However, when the zinc concentrate contains high concentrations of lead and silver, there is a big problem with this process. Because of the “early maturing”, the iron slag is precipitated with the lead silver slag to form a mixed slag, which greatly reduces lead in the slag. , Silver content, making the mixed slag as lead-free raw material unprofitable, need to be pre-treated to improve the slag containing lead, silver grade can be used, in addition, the mixed slag contains high concentrations of iron and zinc and other valuable components, how to Improving the slag containing lead and silver grades and effectively recovering the valuable components in the slag is an urgent technical problem to be solved. This paper focuses on roasting pretreatment-sulfuric acid leaching to obtain an enriched slag process, recovering iron and zinc for lead, silver recovery and leachate recovery. , copper preparation.

2 test

2.1 test materials

The raw materials were taken from a factory iron and lead silver slag. The chemical composition is shown in Table 1.

Table 1 Chemical quantitative analysis results of lead and silver slag main elements/%

ingredient Fe2O3 FeO Pb Zn Cu S0 SVI Ag Au

content 33.83 0.31 4.52 3.46 0.25 1.62 12.45 359.1g/t 0.08g/t

From Table 1, it can be seen that most of the iron in the mixed slag is of high price, the content of ferrous iron is very small, the calcine is obtained through high-temperature oxidation and roasting, the divalent iron is also oxidized to trivalent, and the sulfur is mainly in the form of sulfate. It also contains a small amount of elemental sulfur. Due to the incorporation of iron slag, the content of lead and silver in the slag is relatively low. In addition, it also contains a certain amount of zinc and copper, which has a recycling value after being enriched.

The phase composition of iron is mainly iron oxide and iron lanthanum slag. This part of the iron oxide did not dissolve in high leaching, indicating that this part of the iron oxide is a relatively stable phase; the iron lanthanum is due to pre-neutralization. Prematurely formed, this portion of iron hardly dissolves at high leaching. Zinc is composed of a portion of soluble zinc and zinc ironate that is less soluble under low acid conditions. Lead is mainly in the form of insoluble lead sulfate.

In order to recover the valuable components in the mixed slag, it is necessary to separate the iron slag from the lead silver slag. Since the slag from the iron slag is precipitated from the sulfuric acid solution with higher acidity, the stability in the acidic solution is very high. Well, in order to separate the iron slag from lead and silver slag, we must try to destroy the structure of the iron slag. In this study, the pre-roasting method was used to destroy the iron sill structure.

2.2 Principle flow

Mixed slag

Leaching

Concentrated sulfuric acid

Pre-baking

water

filter

Leachate

Lead silver slag

Recover iron, zinc, copper, etc.

2.3 Test principle

There are two structural formulae for the main component iron in the mixed slag, one is in the form of iron oxide crystal form, the other is yellow sodium iron yttrium crystal [AFe3(SO4)2(OH)6, A refers to NH4+, Na+, K+, etc. ] Form exists. The enrichment factor of lead silver slag depends on the leaching rate of iron in the slag. From the chemical properties of iron compounds, it is known that yellow sodium iron yttrium crystals are a very stable structural formula and are chemically stable. Under normal temperature and pressure conditions, no change in properties usually occurs, and even under normal temperature and high acid conditions, decomposition is less likely to occur. The roasting pretreatment causes the mixed slag to decompose under the heated condition to break its stable structure.

In the roasting process, as the temperature rises, the iron slag can be divided into three different reaction histories. The temperature rises to about 265 °C, and the zinc sulfate crystal water in the jarosite slag is removed. The following reaction occurs. formula

ZnSO4•xH2O=ZnSO4 + xH2O

When calcined at about 412 °C, α-Fe2O3 began to appear in the calcined slag. This indicates that the ruthenium crystal lattice is destroyed, the ruthenium crystal water is removed, and α-Fe2O3 begins to form. The corresponding reaction formula is as follows [3, 4]:

2NaFe3(SO4)2(OH)6=Na2SO4•Fe2(SO4)3 + 2Fe2O3 +6H2O (2)

When calcined at about 670 °C, the content of α-Fe2O3 in calcined slag increased, indicating that decomposition of sulphate intensified and a large amount of α-Fe2O3 crystals formed. The reaction formula is as follows:

Na2SO4•Fe2(SO4)3=Na2SO4+Fe2O3+3SO3

The Na2SO4, Fe2(SO4)3, and ?-Fe2O3 produced in the roasting process are dissolved in a solution with a certain degree of acidity, so that the remaining amount of the mixed slag is greatly reduced, and lead and silver are enriched to a large extent.

2.4 Test methods

Pre-baking treatment: 200 g dry iron/lead silver mixed slag is placed in the muffle furnace, the furnace temperature is controlled in the range of 400~600°C, and the roasting time is 0.5~2h.

Acid leaching: 200 g of pre-calcined mixed slag is 1:1 or 1:1.5 in solid-liquid ratio, concentrated sulfuric acid is 35-40 mL/100 g slag, leaching time is 1 to 2 h, and the reaction is rapid. At the end, add a small amount of NaCl, filter, wash and dry.

3 Results and Discussion

3.1 Pre-baking

The basis for judging the pre-baking treatment to meet the requirements is determined by observing the color change of the lead silver slag. When the color of the lead-silver slag is completely changed from earth yellow to brick red, the pretreatment is ended. The roasting effect at different roasting temperatures for 1 hour is shown in Table 2.

Table 2 Pretreatment effect of lead and silver slag at different temperatures

From Table 2, it can be found that when the temperature is 300°C, the pretreatment effect is not good, and after the temperature reaches 400°C or more, the pretreatment effect is quite good, and the slag weight loss rate is about 15 to 19%. Excessively high temperatures will lead to an increase in the rate of weight loss, accompanied by the decomposition of too many compounds, resulting in a large amount of exhaust gas, such as the decomposition of sulfate, which will lead to environmental deterioration. From the energy point of view, the temperature is too high and the energy consumption increases. Big. Therefore, the pretreatment temperature can be 500°C or 600°C.

Figure 2 shows the effect of calcination time at 600 °C on the slag rate after roasting. It can be seen that the weight loss of slag is basically suspended after roasting for 1 to 1.5 hours, and the roasting process is basically completed. Therefore, 1 to 1.5 hours is selected as the roasting time.

Figure 2 Effect of roasting time on slag rate

3.2 Acid leaching

The residue after roasting pretreatment was leached with sulfuric acid, and the effect of acid leaching temperature, acid amount, acid leaching time, and NaCl on the leaching effect was investigated.

3.2.1 Leaching temperature

Condition setting: After 200g of lead silver slag was pre-baked, the concentration of concentrated sulfuric acid was 80mL and the leaching time was 2h. The effect of leaching temperature on the enrichment effect was examined.

As can be seen from Figure 3, after pre-calcining treatment, the increase of leaching temperature is beneficial to increase the leaching rate of Zn and Fe, and to reduce the slag rate. When the temperature reaches above 90°C, the leaching rate of Zn and Fe and the slag production rate are basically stable. The amount of residual acid and leaching rate showed the opposite trend. The higher the leaching rate, the higher the sulfuric acid consumed by the valuable component and the acid and the lower the amount of residual acid. After the leaching temperature reaches above 90°C, the leaching rate of Zn and Fe is about 95%. Considering many factors such as energy consumption, 90°C is chosen as the acid leaching temperature. The leaching rate after leaching is very low, both below 13%. Lead and silver in the mixed slag have been enriched to a large extent. The enriched slag components are shown in Table 3.

Fig. 3 Effect of temperature on leaching rate, slag rate and residual acid amount of zinc and iron

Table 3 Contents of major components in enriched slag at different temperatures/%

3.2.2 Sulfuric acid dosage

Condition setting: After 200g of lead silver slag is pre-baked, the leaching time is 2h, and the leaching temperature is controlled at about 95°C. The effect of the amount of sulfuric acid on the enrichment effect is examined.

From Fig. 4 and Table 4, it can be found that with the increase of the amount of sulfuric acid, the leaching rate increases and the slag production rate decreases. When the amount of sulfuric acid is more than 70 mL, the leaching rate of iron is more than 95%, and the leaching rate of zinc is more than 90%. When the amount of acid used is more than 70 mL, the enrichment factor of lead and silver in the enriched slag is obvious, the lead content is up to 30%, and the silver content is up to 3 kg/t. Therefore, the amount of concentrated sulfuric acid can take about 70mL.

Fig.4 Effect of sulfuric acid dosage on leaching rate, slag rate and residual acid amount of zinc and iron

Table 4 Analysis of the composition of the main elements in the enriched slag under different amounts of sulfuric acid

3.2.3 Leaching time

Condition setting: after 200g of lead silver slag is pre-baked, the concentration of concentrated sulfuric acid is 80mL, and the leaching temperature is controlled at about 95°C. The effect of leaching time on the enrichment effect is examined.

From Figure 5 and Table 5, it can be seen that with the increase of the leaching time, the leaching reaction is favored. When the leaching time is more than 1.5h, the zinc leaching rate rises above 90%, the leaching rate of iron is about 97%, and the slag production rate is less than 10%, indicating that the enrichment factor of lead silver is about 10 times. Therefore, the leaching time can be more than 1.5h.

Fig. 5 Effect of leaching time on leaching rate of zinc and iron, slag rate and remaining acid amount

Table 5 Analysis of the composition of the main elements in the enriched slag at different leaching times (%)

3.2.4 Sodium chloride

As a result of roasting pretreatment, not only changes in the phase structure of some of the iron, but also changes in other elemental phases. For example, silver is mainly present in the Ag2S phase before treatment, and when it is treated, it will convert some of the Ag2S phase to Ag2O or In the other phases, during the leaching process, Ag2O reacts with the sulfuric acid to form Ag2SO4. Ag2SO4 has a certain solubility in the solution, which causes the silver to enter the solution, which reduces the slag inclusion rate of silver. Therefore, no NaCl leaching and slag addition after roasting will be added. The silver leaching rate of 0.5% NaCl was compared, as shown in Table 6. It can be seen from Table 6 that when NaCl is added during the leaching process, silver is significantly inhibited from being lost to the leachate, and the silver slag inclusion rate is greatly increased.

Table 6 Effect of NaCl on Silver Slagging Rate

3.3 Comprehensive conditions test

Take 1kg of calcined at 600°C for 1.5h to obtain the pretreated slag that is leached at a liquid-solid ratio of 1:1, a concentrated sulfuric acid dosage of 350 mL, sodium chloride 5 g, a temperature of 95° C., and a reaction time of 2 h. The results obtained are shown in Tables 7 and 8.

Table 7 Main components of leachate / g•L-1

Table 8 Analysis of the main elements of raw materials and enriched slag /%

From Tables 7 and 8, it can be found that the results of the comprehensive amplification test are basically the same as those obtained by the small experiment. The leaching rates of zinc and iron in the mixed slag are all higher than 94%. Lead and silver in the mixed slag have been significantly enriched and can be used as lead-added raw materials.

4 Conclusion

Lead silver slag is pretreated by medium-temperature roasting, which effectively improves the partial phase structure of the main elements in the slag, and converts the sodium yellow iron yttrium crystals into ferric sulfate or other crystal forms, which is beneficial to dissolution in acid. Medium temperature roasting pretreatment temperature control range of 500 °C ~ 600 °C, roasting time 1 ~ 1.5h. The acid leaching conditions are as follows: after pretreatment of 200g lead silver slag, the leaching temperature ranges from 90°C to 95°C, the liquid to solid ratio is from 1 to 1.5:1, the concentrated sulfuric acid dosage is from 70 to 80 mL (close to the theoretical acid consumption), and the leaching time 1.5 or

2h, near the end of the leaching, 1 g of NaCl was added. After the filter residue is washed and dried, the slag production rate is less than 13%, the enrichment factor of lead and silver is more than 8 times, sometimes even more than 10 times, the lead content in the enriched slag can reach 30%, and the silver can reach 3kg/t. The collection effect is very good. It can be used as lead-smelting raw materials to comprehensively recover lead and silver.

references

[1] Editorial Board of Lead and Zinc Metallurgy, Lead and Zinc Metallurgy, Beijing: Science Press, 2003