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Scientific Reports volume 14, Article number: 30153 (2024 ) Cite this article cerium acetyl acetomate
Secondary zinc oxide dust is rich in high-grade metals such as Zn, In, Pb, and Ga, and in the face of the depletion of ore resources at home and abroad, it is of great significance to seek an efficient process to realize the full resource recovery of valuable metals in secondary zinc oxide dust. In this study, on the basis of the thermodynamic analysis of the wet treatment process, three wet treatment methods, namely “low acid leaching”, “high acid leaching” and “chlorination leaching”, were used to explore the suitable parameters for stepwise extraction of Zn, In and Pb metals. The results showed that the three wet treatment methods could effectively extract the corresponding main elements, and the optimal leaching rates of Zn, In and Pb were 73, 90 and 94%, respectively. Thermodynamic analysis shows that under ideal conditions, the “cascade separation” of some or all metals can be theoretically achieved by using a suitable leaching solvent for zinc oxide dust. The concentration of sulfuric acid, the ratio of liquid solid volume to mass and temperature had great effects on the leaching rate of Zn and In, and the leaching rate of Zn and In also increased with the increase of the values of the three experimental parameters, which was positively correlated. The leaching rate of Pb will increase with the increase of sulfuric acid concentration, but when the pH of the solution system is < 2, Pb will form PbSO4 precipitate, which inhibits the leaching ability of Pb. In the chlorinated leaching system with “ammonium chloride + hydrochloric acid” as the leaching solvent, the excess Cl− and Pb2+ fully coordinated to promote the efficient leaching of Pb metal, and the initial pH value of the solution had a great influence on the Leaching Rate of Pb. The multi-stage combined wet treatment process is an effective solution to realize the full quantitative recovery of valuable elements in Secondary zinc oxide dust, In this paper, the suitable process conditions for stepwise extraction of Zn, In and Pb metals were obtained through wet treatment experiments, and the cascade separation of metals in zinc oxide dust was preliminarily realized, which provided an important idea for the efficient utilization of metallurgical dust and sludge solid wastes, and at the same time provided theoretical support for the industrial practice of recycling valuable elements in metallurgical dust.
The steel production process is resource- and energy-intensive, with large production scale and material flow, and long process flow, resulting in a large amount of solid waste, which has become a recognized major source of industrial solid waste. Metallurgical dust is one of the unavoidable solid wastes in the process of steel production, and is the second largest metallurgical solid waste after metallurgical slag, generally accounting for about 8%~10% of crude steel output1,2, which comes from various processes of steel smelting, mainly including sintering, blast furnace ironmaking, converter steelmaking, electric furnace steelmaking and steel rolling3, It is rich in valuable metals such as Zn, Pb, In, and Ga, and has great recycling value. In the face of the current situation of reducing high-grade ore sources, depleting rich ore resources, and rising iron ore prices in the iron and steel industry4, it is imperative to seek a new process of whole-process treatment and realize the full resource recycling and utilization of metallurgical dust5.
At present, the mainstream processes for the treatment of metallurgical dust solid wastes include direct back sintering treatment6,7,8, physical treatment9,10, pyrometallurgical treatment11,12,13,14,15, and wet treatment16,17,18. The direct back sintering treatment process is one of the processes commonly used by iron and steel enterprises in the early days, which has the advantages of simple operation and small investment cost, but due to the wide variety of metallurgical dust and large fluctuations in composition, it is easy to cause the deterioration of sinter quality; At the same time, metallurgical dust contains more elements such as K, Na, Zn, etc., which can not be effectively removed in the sintering process, and after entering the blast furnace smelting again, the problem of unsmooth blast furnace production caused by the enrichment of harmful elements has not been effectively solved, and the process has been basically discontinued. Although the extraction of valuable elements from metallurgical dust by pyrometallurgical process has entered the industrial stage, there are still some problems in the stepwise extraction of valuable elements from multi-source metallurgical dust, such as the fine particle size of dust, the particle wrapping of different dusts and after mixing, the uneven distribution of chemical components, the unclear volatilization process of valuable element reduction, the unclear selective reduction mechanism of different valuable elements under the synergistic effect of multi-source metallurgical dust, and the serious ringing of the reactor kiln caused by volatile deposition. The wet treatment process mainly includes acid leaching method, alkaline leaching method, chlorination leaching method, biological leaching method, etc., select the appropriate leaching agent and metallurgical dust to have a chemical reaction to promote the separation of target metal elements, and then purify the leaching solution and use electrolysis, replacement, extraction and other processes to extract the main element metal, which has the advantages of strong selectivity, high product grade and good recovery effect. However, there are still problems in wet treatment, such as high requirements for raw materials (only suitable for the treatment of medium and high zinc dust), complex treatment process, single and highly targeted extraction elements, and easy to cause secondary pollution (serious acid and alkali pollution, difficult to treat waste liquid), etc., and it is urgent to develop a new type of wet treatment solvent with “high selection, zero pollution and low cost”.
On the whole, the metallurgical dust recovery process is diverse and highly targeted6, and there are generally shortcomings such as relatively single recovery elements, poor co-processing ability, and high treatment cost19, and there is a serious lack of effective connection and reprocessing capacity between processes, which cannot effectively use the advantages of each process to realize the full resource recycling of metallurgical dust, and it is urgent to seek a new whole-process treatment process that breaks through the technical bottlenecks and barriers between processes. Therefore, combined with the new trend of existing process development20,21, a new idea of the whole process of “pyrometallurgical enrichment-wet separation-tailings recycling” for multi-source metallurgical dust treatment was proposed. The zinc oxide dust enriched by the pyrotechnic method was selected as the experimental raw material, and the multi-stage combined wet treatment process of “low acid leaching-high acid leaching-chlorination leaching” was formulated through the thermodynamic analysis results of the wet treatment process, and the suitable process conditions for stepwise extraction of Zn, In and Pb metals were obtained, and the cascade separation of zinc, indium and lead metals in the zinc oxide dust was initially realized, which provided practical support for the realization of the full resource utilization of valuable elements in metallurgical dust.
The specific models and manufacturers of the reagents and equipment used in the experimental process and later sample testing are shown in Tables 1 and 2.
H2SO4 was selected as leaching agent for acid leaching of Zn and In metals, and NH4Cl + HCl was selected as leaching agent for chlorinated leaching of Pb metals. The control variable method was used to prepare sulfuric acid and ammonium chloride solutions according to the predetermined liquid-to-solid mass ratio, and placed in a 500 mL volumetric flask for later use. Weigh 10 g of sample, slowly add it to the beaker, put the dry magnetic rotor into the beaker and add a certain amount of sulfuric acid solution or ammonium chloride solution, wrap the top of the beaker with plastic wrap, turn on the stirring and timing, start the experiment, monitor the temperature and pH value in the leachate in real time and adjust; After the leaching reaches a predetermined time, the stirring is stopped and the rotary vane high vacuum pump (2FY-4 C-N) is used to pump the filtration while it is hot; The leachate was placed in a centrifuge tube for measurement, the leached residue was washed with an equal volume of deionized water and filtered, and then placed in an electric blast drying oven for constant temperature (12 h at 105 ± 5 °C), after which the samples were weighed and tested.
At the end of the leaching experiment, the leaching solution was diluted according to the content gradient of each metal element in the raw material and the leaching residue, loaded into the corresponding centrifuge tube, and the mass concentration of the metal element (g/L) was determined by ICP-MS, and the leaching rate of each metal was calculated according to the theoretical volume of leaching, and the calculation method is shown in Eq. (1). The leaching rate of lead, iron and silver metals in chlorinated leaching is calculated based on leaching residue, and the calculation method is shown in Eq. (2).
In the relational equation:xB—Leaching rate of metals (Zn, Fe, Pb, In) in %;yB—Leaching rate of metals (Fe, Pb, Ag) in %;ρ—Mass concentration of metals (Zn, Fe, Pb, In) in leach solution, g/L ;V—Volume of leachate, mL;mB—Mass of raw material, g;w—Mass fraction of metals (Zn, Fe, Pb, In) in raw material, %;n—Dilution of leaching solution;m1—Mass of raw material for chlorinated leaching, g;m2—Mass of leaching residue from chlorinated leaching, g; w1—Mass fraction of metals (Fe, Pb, Ag) in chlorinated leaching material, %w2—Mass fraction of metals (Fe, Pb, Ag) in leachate from chlorinated leaching,%.
The secondary zinc oxide dust used in the experiment was pale yellow in colour and was subjected to XRF physical composition analysis to obtain the chemical composition of each element, the results are shown in Table 3.
Due to the extremely low content of rare metals In, Rb, Sn and Ga, their oxides could not be analyzed effectively. In order to accurately obtain the chemical composition and content of rare metals in the sample, the ICP-MS method was used for analysis, and the results are shown in Table 4.
XRF and ICP-MS results showed that the main chemical components of zinc oxide dust were Zn, Fe, Na, Pb and K, and their oxide content was 73.61 wt%. The non-metallic Cl content accounted for 20.19 wt%; The dispersed metals In, Rb and Ga accounted for 0.014 wt%, 0.156 wt% and 0.010 wt%, respectively.
The zinc dioxide dust was analyzed by laser particle size, and the results are shown in Fig. 1. It can be seen from Fig. 1 that the particle size distribution of zinc dioxide dust is within 0.224 ~ 158.866 μm, and the distribution range is wide; Particles with a size smaller than 1 μm accounted for about 10 per cent of the volume, and particles larger than 25.179 μm accounted for about 3 per cent of the volume, with a small index of the dust coarse end particle size; When the particle size was 3.17 μm, the cumulative particle size volume distribution was 50%, and the specific surface area of the dust raw material was large, which was 2310 m2/kg.
Particle size distribution of secondary zinc oxide dust.
From the analysis of XRD detection in Fig. 2, it can be seen that the main physical phases of zinc in the secondary zinc oxide dust are ZnO, ZnFe2O4, InAl3(ZnO)x and so on; The main physical phase of lead is Pb2O3, and according to literature22, Pb in this type of dust also exists as the mineral phase of PbS; The physical phase of iron is mainly Fe2O3. Indium metal has a strong affinity for sulfur, and indium vapor volatilization is mainly embedded in complex mineral phases such as zinc-containing spinel iron during the enrichment process of zinc oxide dust, so indium mainly exists in the physical form of ZnFe2O4 and InAl3(ZnO)x. According to literature23,24, indium is also present in the mineral phase of In2S3 in the raw material of dust; Alkali metals such as potassium and sodium are mainly in the form of chloride salts, and some potassium metals exist in the form of mineral phases of KFeO2.
XRD diffraction pattern of secondary zinc oxide dust.
Field emission scanning electron microscopy (SEM-EDS) was used to observe the micro-morphological features of the samples, and the detection results are shown in Fig. 3; at the same time, they were analysed by EDS-Mapping, and the results are shown in Fig. 4. From Fig. 3A, B and C, it can be seen that the secondary zinc oxide dust is generally in the form of lumps or long cubes. The zinc oxide dust was scanned at two sample points 1 and 2 and the contents of Zn, Pb and In metals were quantitatively analyzed (Fig. 3D,E), and it can be seen that the Zn mass fraction was high, the highest was 70.76%, and the In mass fraction remained at (20 ± 5)%, Zinc-indium metal has a pronounced ‘bundling’ effect, mainly due to the fact that some of the indium is attached to the interior or surface of the zinc mineral phase. As can be seen from Fig. 4, the energy spectral densities of metals such as Zn, K, Na, Fe, Pb and non-metals Cl are higher, and the energy spectral densities of dilute metals such as In are lower, which proves the results of the chemical composition test; the higher energy spectral densities of the non-metals O and Cl indicate that most of the metals contained in the secondary zinc oxide dust exist in the form of oxides or chlorides; In addition, the detection of non-metallic S in the sample indicates that some metals may exist in the form of sulfides, such as ZnS, InS and other mineral phases, which are more difficult to leach mineral phases, and the leaching parameters need to be improved to achieve enhanced leaching effect. Combined with XRF, ICP-MS chemical composition and SEM-EDS detection results, it can be seen that the order of metallic elements in secondary zinc oxide dust is Zn > K > Fe > Pb > Na > In, and the order of non-metallic elements is O > Cl > Si > S.
SEM-EDS analysis of secondary zinc oxide dusts. (A), (B)—20 μm and 10 μm surface scans of the sample; (C)—1 μm stock spot scanning; (D), (E)—EDS peak patterns of sampling points 1 and 2 in C.
EDS spectrum analysis of secondary zinc oxide dust.
The experiment focused on the leaching effect of zinc, lead, iron and dilute metal indium with high content in zinc oxide dust, and sulfuric acid and ammonium chloride were used as leaching agents, respectively. In order to reveal the thermal variation law and feasibility of the reaction between the main phases of each metal and the sulfuric acid solution during the leaching process of zinc oxide dust, the thermodynamic analysis was carried out from two perspectives: the variation law of Gibbs free energy with temperature and the variation law of Potential-pH equilibrium diagrams25of the leaching system. The variation of Gibbs free energy (ΔGT) of the leaching system with temperature was calculated by the Reaction module of the thermodynamic software FactSage 8.3, and the spontaneity and difficulty of the reaction between the main phases of each metal and the sulfuric acid solution in the zinc oxide dust were analyzed. The EpH module in the thermodynamic software FactSage 8.3 plotted the Potential-pH equilibrium diagrams of the leaching system with pH value, and explored the optimal experimental scheme for efficient leaching of zinc, indium and lead.
The chemical equations for the direct reaction of zinc, iron, lead and indium metal phases with sulfuric acid are shown in Table 5. In the range of 25 ~ 100 °C, the variation curves of Gibbs free energy (ΔGT) with temperature (T) of each chemical reaction are shown in Fig. 5.
Variation curves of Gibbs free energy with temperature in the main phases of Zn, Pb, In, and Fe metals.
From the results of thermodynamic analysis in Fig. 5, it can be seen that under the ideal state (standard air pressure, single metal oxide leaching system), the reaction temperature is set in the range of 25 ~ 100 °C, the Gibbs free energy of the reaction formula (1)~(12) is less than 0, and the main mineral phases of zinc (ZnO, ZnFe2O4, ZnS), iron (Fe2O3, ZnFe2O4), lead (Pb2O3, PbS) and indium (In2O3, In2S3) can chemically react with sulfuric acid. Moreover, the absolute value of the standard Gibbs free energy of the reaction was greater than 40 kJ/mol26, indicating that all reactions could be carried out spontaneously, and the leaching temperature was increasing, and some of the Gibbs free energy showed a gradual increasing trend.
In order to study the leaching law of secondary zinc oxide dust in the same leaching environment and obtain a suitable hierarchical leaching scheme, the thermodynamic analysis of Zn, Pb, In and Fe metals in the leaching system was carried out, and the Potential-pH equilibrium diagrams of 25, 60, 80 and 90 °C were plotted, as shown in Fig. 6.
Potential-pH equilibrium diagrams of Zn-Fe-In-Pb-S-H2O system. A—25℃;B—60℃;C—80℃;D—90℃
It can be seen from Fig. 6 that the main mineral phase forms of Zn, Fe, Pb and In can undergo chemical reactions in the temperature range of 25 ~ 90 °C, but the pH value range required for leaching varies greatly. Compounds such as ZnO and FeO can be converted to Zn2+ and Fe2+ at pH < 6, while the main phase of Pb and In reacts with sulfuric acid solution at a very low pH, which is very low. It shows that under the same leaching environment, if the lead and indium metals in the secondary zinc oxide dust are leached, the mass concentration of sulphuric acid in the leaching system needs to be increased accordingly to ensure that the leaching solution is strongly acidic. In addition, the effects of leaching temperature on the four metal-related mineral phases were different, and the pH value of the solution required for the leaching reaction of Zn phase decreased with the increase of temperature, which was negatively correlated. The pH value required for the leaching of Pb-related mineral phase increased with the increase of temperature, indicating that the increase of temperature could significantly increase the activity of Pb phase and reduce the acidity requirement of the solution. The leaching reaction of Fe2+-related mineral phases contradicts the conclusion of Pb. In the leaching reaction of In- and Fe-related phases, the pH required for the solution is less affected by temperature.
On the basis of a comprehensive analysis of the physical and chemical properties of zinc oxide dust, combined with the variation of Gibbs free energy with temperature and Potential-pH equilibrium diagrams in the leaching system, the experimental scheme for cascade leaching of zinc, indium and lead is shown in Fig. 7.
Stepwise leaching protocol for Zn, In and Pb secondary zinc oxide dusts.
The control variable-single-factor method was used to explore the effects of sulfuric acid concentration, liquid-solid volume mass ratio, leaching time, leaching temperature, stirring speed, leaching times and other factors on the leaching behavior of Zn, Pb, In and Fe metals. According to the content characteristics of each metal in zinc oxide dust and the summary analysis of related literature research27,28,29, the reference conditions for low acid leaching experimental parameters were set as sulfuric acid mass concentration 100 g/L, liquid-solid volume mass ratio 6 mL/1·g, leaching time 90 min, leaching temperature 50 °C, stirring speed 500 r/min, and the setting of experimental variables in the later stage were optimized and adjusted up and down this reference condition, and the variation range and interval of each parameter are shown in Table 6. The results of the low acid leaching experiment are shown in Fig. 8, and the analysis results of the main components in the high acid leaching solution under the optimal parameters are shown in Table 7.
It can be seen from Fig. 8 that the mass concentration of sulfuric acid, the mass ratio of liquid to solid and the leaching temperature have great effects on the leaching of Zn, In and Fe in the low acid leaching experiment30. Zn is the main element in the raw material of zinc oxide dust, and the mass is relatively high, and when the concentration of H+ is low, the sulfuric acid mainly reacts with the phase of Zn metal related substances. With the increasing concentration of sulfuric acid, Fe and In began to participate in the reaction. In order to achieve the best extraction effect of Zn and the best enrichment effect of Pb and In, the concentration of sulfuric acid should not be set too high in the experiment. The liquid-solid volume mass ratio is one of the key factors affecting the leaching effect, with the increasing ratio, the free H+ in the solution increases, the leaching rates of Zn, Fe and In all show an increasing trend, and the increase of Zn is obvious. Due to the increase of the proportion, the pH of the solution decreases, and most of the Pb is inhibited from leaching to form sulfate precipitation, so the Pb leaching rate in the whole process is close to 0. The effects of leaching temperature and stirring speed on the metal leaching effect are similar, and with the increasing value of the two, the effective collision between H+ and the metal increases, which is conducive to breaking the chemical bond in the metal phase and promoting the increase of the metal leaching rate. In the process of increasing temperature, the metal phase gradually decomposes, the particle size of the zinc oxide dust is further reduced, the specific surface area increases, the contact chance between the leaching agent and the metal increases, the reaction probability increases, and the leaching rates of Zn, In and Fe all show an increasing trend, but in order to achieve the best leaching effect of Zn and the best enrichment effect of Pb and In, it is necessary to reasonably adjust the experimental parameters.
Effect of different low acid leaching parameters on Zn leaching rate.
The comprehensive experimental results showed that the suitable process conditions for achieving efficient leaching of Zn and efficient enrichment of In and Pb were sulfuric acid concentration of 100 g/L, liquid-solid volume mass ratio of 5 mL/1·g, leaching time of 90 min, leaching temperature of 60 °C, stirring speed of 500 r/min, and zinc leaching rate of more than 70 wt% in one leaching. The indium mass fraction increased to 0.052 wt%, achieving a 3.71-fold enrichment effect, and the lead mass fraction increased to 10.8 wt%, achieving a 2.45-fold enrichment effect.
The raw materials used in the experiment were the leaching residue after drying after the low-acid experimental treatment, and the effects of sulfuric acid concentration, liquid-solid volume mass ratio, leaching time, leaching temperature, stirring speed and other factors on the leaching behavior of lead and indium were mainly investigated. On the basis of a large number of pre-experiments, the reference conditions for setting the parameters of high acid leaching experiment were sulfuric acid mass concentration 180 g/L, liquid-solid volume mass ratio 6 mL/1·g, leaching time 4 h, leaching temperature 80 °C, stirring speed 500 r/min, and the setting of experimental variables in the later stage was optimized and adjusted up and down this reference condition, and the variation range and interval of each parameter are shown in Table 8. The results of the high-acid leaching experiment are shown in Fig. 9, and the analysis results of the main components in the high-acid leaching solution under the optimal parameters are shown in Table 9.
Effect of different high acid leaching parameters on In leaching rate.
It can be seen from Fig. 9 that the mass concentration of sulfuric acid, the mass ratio of liquid to solid volume, and the stirring speed have great effects on the leaching of In the high acid leaching experiment31,32. When the concentration of sulfuric acid increased to 170 g/L, the In leaching rate was higher at 91.94%, and then decreased. Because the Cl content of non-metallic elements in the leaching slag is greatly reduced after the low acid leaching experiment, and the leaching solution is rich in more \(\:{\text{S}\text{O}}_{4}^{2-}\) , and the chlorinated leaching environment conducive to Pb leaching is not formed, so the increase of sulfuric acid mass concentration and liquid-solid volume mass ratio has little impact on the Pb leaching rate, and will waste more sulfuric acid solution, increasing the cost of industrialization in the later stage, and the best parameter conditions need to be reasonably determined according to the predetermined goals. The leaching time had little effect on the leaching rate of Pb and In. With the increase of leaching temperature, the In leaching rate increased slowly, and was higher at 80 °C, which was 93.43%, and continued to increase the temperature, and the In leaching rate decreased slowly. The leaching temperature had little effect on the Pb leaching rate, and with the increase of the leaching temperature, the Pb leaching rate was almost 0. With the increase of temperature, the movement rate of each ion in the leaching system accelerates, and the effective collision probability of H+ in sulfuric acid and each metal compound also increases, and the best effect is achieved when the leaching temperature rises to 80 °C. However, if the temperature is too high, the relative effect on the leaching rate of each metal will gradually decrease33, and on the contrary, it will cause the leaching solution to gradually “boil”, causing some H+ to splash on the wall of the beaker, resulting in the reduction of the leaching rate of each metal.
The comprehensive experimental results showed that the suitable process conditions for achieving high efficiency leaching and Pb enrichment were as follows: sulfuric acid concentration of 170 g/L, liquid-solid volume mass ratio of 7 mL/1·g, leaching time of 4 h, leaching temperature of 80 °C, stirring speed of 500 r/min, the optimal leaching rate of In was more than 90%, and the Leaching rate of Pb was only 0.56%. The mass fraction of Pb metal in the sample increased from 4.47 to 40.12%, and the overall enrichment effect was 8.86 times.
The raw materials used in the experiment were the leaching slag of indium metal after high acid leaching, and the influence of pH value, leaching temperature, chloride ion concentration, liquid-solid volume mass ratio, leaching time and other factors on the leaching behavior of lead, iron and silver metals was investigated. On the basis of a large number of pre-experiments, the reference conditions for setting the chlorination leaching experimental parameters were the initial pH value of the solution 3, the liquid-solid volume mass ratio of 10 mL/1·g, the chloride ion concentration of 6 mol/L, the leaching time of 2 h, the leaching temperature of 80 °C, and the stirring speed of 500 r/min, and the setting of the experimental variables in the later stage was optimized and adjusted up and down this reference condition, and the change range and interval of each parameter are shown in Table 10.
“Ammonium chloride + hydrochloric acid” was used as the leaching agent for the chlorination leaching experiment (analytical pure, Tianjin Yongda Chemical Reagent Co., Ltd.), and the water was deionized water; When there is an excess of chloride ions in the solution34,35, the lead and silver-related metal ions will carry out coordination reaction with them to generate complex ions that are easily soluble in the chlorinated leaching system36,37, and hydrochloric acid can adjust the pH value of the leaching solution, inhibit the leaching of iron and other related impurity ions, and promote the efficient selective leaching of lead, silver and other target metals. The results of chlorination leaching experiments are shown in Fig. 10, and the analysis results of the main components in chlorinated leaching slag under the optimal parameters are shown in Table 11.
Effect of different chlorination leaching parameters on Pb leaching rate.
As can be seen from Fig. 10, the initial pH value of the solution and the ratio of liquid-solid volume mass have a great influence on the leaching rate of Pb, Ag and Fe in the chlorination leaching experiment. When the pH value of the solution was 3, the leaching rates of lead and silver reached the maximum, which were 92.8% and 91.94%, respectively. With the continuous increase of the pH value of the leaching system, the leaching rate of lead and silver showed a decreasing trend, because when the pH value was low, the coordination ability of lead, silver ions and chloride ions was enhanced, and the lead was quickly dissolved into the leaching solution from the high-acid leaching indium slag, and with the increase of the pH value of the solution, the coordination ability of the two ions gradually weakened, which made the leaching rate decrease, and the results of the leaching thermodynamic analysis were verified. The iron metal remained at a low level within the range of the experimental pH value, and the iron leaching rate decreased with the gradual increase of the pH value of the solution, which was due to the increase of the pH value, the solution gradually transformed from strong acidity to weak acidity, and the iron ion hydrolysis reaction was greater than the leaching reaction, resulting in the gradual decrease of the iron ion content in the leaching solution. With the increase of leaching temperature, the leaching rates of lead and silver increased rapidly34,38. When the leaching temperature increased to 80 °C, the lead leaching rate increased to the highest (91.5%), and the leaching rate continued to increase, and the leaching first tended to be flat, and then gradually decreased39. The leaching reaction of lead is mainly a solid-liquid two-phase reaction, and increasing the temperature will increase the activity of the leaching slag raw material, improve the leaching reaction efficiency, and indirectly increase the leaching rate of lead metal, but the higher the temperature, the more likely it is to cause the leaching solution to boil and splash, resulting in the unreacted material sticking to the wall edge of the beaker, and also indirectly increasing the energy consumption of the experiment, therefore, the leaching temperature should be 80 °C. The effect of chloride ion concentration on the leaching rate of lead, iron and silver is similar to that of leaching temperature. The liquid-solid volume mass ratio has a great effect on the leaching rate of lead and silver, but has almost no effect on iron leaching. With the increase of the liquid-solid mass ratio, the leaching rate of lead and silver increased, especially the increase of silver leaching rate, when the liquid-solid mass ratio increased to 12 ml/1·g, the growth efficiency decreased, and the leaching rate gradually flattened. The iron leaching rate was relatively stable, maintaining a level of 15 ± 5%. However, it must be considered that an excessive liquid-to-mass ratio will significantly reduce the concentration level of lead and silver ions in the leaching solution, and is not conducive to the subsequent recovery of lead and silver metals40. The leaching time had little effect on the leaching rate of the three metals.
The comprehensive experimental results showed that the suitable process conditions for the efficient leaching of Pb metal by chlorination leaching treatment of high acid leaching slag were the initial pH value of the solution 3, the volume ratio of liquid to solid volume 12 mL/1·g, the chloride ion concentration of 7 mol/L, the leaching time of 2 h, the leaching temperature of 80 °C, the stirring speed of 500 r/min, and the optimal leaching rate of lead was more than 93%, showing a good leaching effect.
The physical and chemical properties of secondary zinc oxide dust, low acid leaching zinc slag, high acid leaching indium slag and chlorinated leaching lead slag were compared and analyzed, and the experimental effect of secondary zinc oxide dust classification leaching was comprehensively verified, including chemical composition and content, main metal mineral phases and microscopic morphology.
As can be seen from Fig. 11, for the problems such as the large amount of Zn in the secondary zinc oxide dust and more impurity components, the first choice of low-acid leaching has a significant advantage, on the one hand, the mass fraction of Zn in the sample is reduced from 50.8 wt% to 23.6 wt%, which reduces the influence of a large amount of Zn2+ on the subsequent indium high-acid leaching and lead chloride leaching processes; On the other hand, the In content in the sample was increased from 0.014 wt% to 0.052 wt%, which provided the best raw material for the high acid leaching of In. After the high acid leaching experiment of Indium, the Pb metal was enriched to a larger extent, and the mass fraction was increased from 4.4 wt% to 40.1 wt% of the raw material; By high acid leaching, the In content decreased from 0.052 wt% to 0.001 wt%, indicating that the high acid leaching experiment of indium has a better effect. The Pb metal mass fraction decreased significantly after the chlorinated leaching experiment of Pb, indicating that the chlorinated leaching experiment of Pb has a better effect. The overall experiment flexibly applies the special requirements of In and Pb metal leaching, which not only reduces the impurity components of the leaching solution, but also obtains better experimental raw materials in turn, and initially realises the classification and recovery of Zn, Pb and In metals.
Comparison of the metal contents of Zn, Pb, In and Fe in the raw materials and three types of leaching slag.
XRD diffraction patterns of the samples before and after experimentation.
As can be seen from Fig. 12, after the low acid leaching experiment, the main mineral phase morphology of each metal was changed, the oxide strength of Zn was significantly reduced, and it mainly existed in the form of sulphide or ZnFe2O4 and other complex spinel phases; the chlorides of alkali metals K and Na disappeared; and the metals, such as In and Pb, mainly existed in the form of sulphide. After the high acid leaching experiment, each metal oxide phase basically disappeared, and the metal phases represented by Zn and Pb were all converted to sulphide forms, and the In metal phase disappeared, indicating the effectiveness of the indium high acid leaching experiment. After the chlorinated leaching experiment, the sulfide intensity of Pb was significantly reduced, and the sulfide intensity of Zn and Fe was further reduced, indicating the effectiveness of the lead chlorinated leaching experiment.
As can be seen from Fig. 13, after the low acid leaching experiment, the lumpy and elongated particles in the secondary zinc oxide dust were obviously reduced, and the number of small particles of dust decreased, but some particles still retained their original morphology, which was presumed to be the remaining insoluble phases such as zinc ferrate and sulphide after the low acid leaching experiment; After the high acid leaching and chlorination leaching experiments, the particle size was further reduced, the individual particles basically disappeared, and only some of the still undissolved solid particles were retained and interlinked, which was presumed to be the leaching process, and some of the incompletely reacted small particles of leaching residue attached to the surface of the insoluble phase (ZnFe2O4) or the precipitate.
Comparison of the microscopic morphology of the samples before and after the experiment at magnifications of 20 μm, 10 μm, and 5 μm. (A), (B), (C)-secondary zinc oxide dust 20 μm, 10 μm, 5 μm plots; (D), (E), (F)-low acid leaching slag 20 μm, 10 μm, 5 μm plots;(G), (H), (I)-high acid leaching slag 20, 10, 5 μm plots; (J), (K),(L)-chlorinated leaching slag 20 ,10 , 5 μm plots
(1)Compared with zinc oxide dust, the zinc oxide dust obtained by pyrometallurgical preliminary enrichment has significant advantages such as less impurity components, excellent particle size performance, simple and easy decomposition of mineral phase composition, and the grade of each major element metal in the dust is extremely high.
(2)The results of thermodynamic analysis of Wet leaching process of secondary zinc oxide dust by the thermodynamic software FactSage 8.3 showed that, under ideal conditions, all the major metals in the dust material could react spontaneously with the sulphuric acid leaching agent; Reasonable control of Wet leaching process parameters (sulfuric acid mass concentration, chloride ion concentration, etc.) can theoretically achieve the “gradient separation” of some or all metals, and a multi-stage combined leaching experimental scheme of “low acid leaching zinc-high acid leaching indium-indium chloride leaching lead” was designed, and the later experimental results showed that the scheme had significant advantages.
(3)The suitable process conditions for low-acid leaching of zinc were sulphuric acid mass concentration of 100 g/L, liquid-solid-volume mass ratio of 5 mL/1·g, leaching time of 90 min, leaching temperature of 60 ℃, stirring speed of 500 r/min, and one-time leaching; The suitable process conditions for high acid leaching of indium were sulfuric acid mass concentration of 170 g/L, liquid-solid product mass ratio of 7 mL/1·g, leaching time of 4 h, leaching temperature of 80 ℃, and stirring speed of 500 r/min; The suitable process conditions for lead leaching by chlorination were initial pH 3, liquid-solid product mass ratio of 12 mL/1·g, chloride ion concentration of 7 mol/L, leaching time of 2 h, leaching temperature of 80 ℃, and stirring speed of 500 r/min; The optimal leaching rates of zinc, indium and lead are 73%, 90% and 94%, respectively, which provides a reference for the full quantitative recovery of valuable metals in secondary zinc oxide dust.
No external data was used for this research. All the generated experimental data are included in this manuscript.The datasets used and/or analysed during the current study available from the corresponding author on reason-able request.
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This paper is supported by the National Natural Science Foundation of China Joint Fund for Regional Innovation Development (U20A20271).
College of Metallurgy and Energy, North China University of Science and Technology, Tangshan, 063210, Hebei, China
Gui-hua WANG, Pei-pei DU, Liang-jin ZHANG, Yue LONG & Jian-song ZHANG
Key Laboratory of Modern Metallurgical Technology of the Ministry of Education, North China University of Science and Technology, Tangshan, 063210, Hebei, China
Gui-hua WANG, Pei-pei DU, Liang-jin ZHANG, Yue LONG & Jian-song ZHANG
General Institute of Construction Research, MCC, Beijing, 100088, China
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Professor Long Yue conceived the overall framework of the paper, Dr. Wang Guihua and Dr. Du Peipei conducted specific experiments and results analysis, and Dr. Zhang Jiansong and Dr. Zhang Liangjin participated in the analysis and revision of the first draft of the paper. The authors would like to thank Dr Du Peipei and Dr Zhang Jiansong for their help.
Correspondence to Pei-pei DU or Yue LONG.
The authors declare no competing interests.
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WANG, Gh., DU, Pp., ZHANG, Lj. et al. Stepwise extraction of zinc, indium and lead from secondary zinc oxide dusts experimental study. Sci Rep 14, 30153 (2024). https://doi.org/10.1038/s41598-024-81667-6
DOI: https://doi.org/10.1038/s41598-024-81667-6
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