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1.INTRODUCTIONElectronic-grade sulfuric acid, commonly referred to as ultra-high-purity sulfuric acid, constitutes an essential foundational chemical reagent in the advancement of microelectronics industry technology. It finds extensive application in the production of large-scale integrated circuits and discrete electronic devices. Its primary application involves its combination with electronic-grade hydrogen peroxide to efficiently eliminate impurity particles, inorganic residues, and carbonaceous matter from the wafer. The consumption of electronic-grade sulfuric acid accounts for approximately 30% of the total high-purity reagents, and it is one of the most widely used chemicals in the semiconductor manufacturing process1,2. At present, the global usage of electronic-grade sulfuric acid reaches 1.5 million tons. After the use of SPM solution, the amount of waste liquid produced reached more than 1.8 million tons. With the transfer of the international semiconductor industry to China, China’s semiconductor consumer market is huge. As one of the most widely used chemicals in ultrapure reagents for semiconductors, electronic-grade sulfuric acid is not only the technological high point in the field of sulfur chemical industry, but also the fastest-growing fine sulfur chemical product. In particular, the large-scale mass production of processes at 28 nm and below imposes increasingly stringent quality requirements on ultra-high-purity electronic-grade sulfuric acid and concurrently doubles its usage. Anticipatedly, the usage of electronic-grade sulfuric acid in mainland China is projected to reach 400,000 tons by the year 2025. Following utilization, electronic-grade sulfuric acid transforms into acidic and hazardous waste liquid, primarily comprising hydrogen peroxide, metal ions, organic matter, and additional impurities. Semiconductor factories all use acid and alkali neutralization before entrusting relevant agencies to dispose of it. This not only has high processing costs and large processing capacity, but also causes a large amount of waste of non-metallic sulfur resources3-6. Currently, there is limited global research on the resource utilization of waste sulfuric acid, and this area remains largely unexplored. This study analyzed the waste sulfuric acid generated by a domestic semiconductor factory and found the primary impurities in the waste electronic-grade sulfuric acid, which include hydrogen peroxide, trace metal ions, and polysulfides. First, electrochemical catalytic oxidation is used to targeted convert polysulfides in waste sulfuric acid, and then chemical and electrochemical methods are used to prepare high-purity copper sulfate. The electrochemical preparation method obtains high-purity copper sulfate with higher purity and lower impurity content. This method accomplishes the cascade utilization and recycling of semiconductor waste electronic grade sulfuric acid. 2.MATERIALS AND METHODS2.1Targeted conversion of polysulfides in semiconductor waste electronic grade sulfuric acidThis study employs ICP-MS, TOC instruments, and chemical analysis methods to assess the concentrations of metal ions, TOC, anions, and other impurities in waste sulfuric acid. Following a 100-fold dilution of the waste sulfuric acid sample, time-of-flight mass spectrometry was employed to quantify the polysulfide content in the solution. The prepared standard solution samples of sodium sulfite, potassium tetrathionate, potassium hydrogen peroxymonosulfate, sodium metabisulfite, sodium thiosulfate and potassium pyrosulfate were measured and analyzed by a quadrupole time-of-flight mass spectrometer on the above samples and the dilute sulfuric acid sample diluted 10 times. 2.2Preparation of high purity copper sulfateThe technical route for preparing high-purity copper sulfate by chemical synthesis was shown in Figure 1. 2.1.1Copper oxide synthesis method I.
2.2.2Copper oxide synthesis method II.The preceding steps are simplified by employing a direct synthesis method without utilizing Cu(OH)2CO3 as a precipitant, and the filtrate is recycled.
2.3Electrochemical preparation methodEquipment: The electrolytic cell features a three-chamber structure, including the anode chamber, the intermediate chamber, and the cathode chamber. The V for these chambers is set at 1:4:1 to 1:6:1. The anode chamber and the intermediate chamber use sulfonic acid cation exchange membranes, and the cathode chamber and the intermediate chamber use a composite membrane layer of proton exchange membrane and microporous polymer membrane composite membrane layer. 1000 mL of the above-mentioned waste sulfuric acid solution for electrocatalytic conversion was taken and it was added to the electrolyzer. A high-purity copper plate as the anode and a titanium plate as the cathode was employed, utilizing an electrode current density ranging from 300 A/m2 to 400 A/m2 for electrolysis. Throughout the electrolysis process, the solution in the middle chamber using a pump was circulated, continuously extracting copper sulfate solution while replenishing dilute sulfuric acid to facilitate the continuous preparation of copper sulfate solution. Subsequently, the electrolyzed copper sulfate to induce crystallization was evaporated, concentrated, and then cooled, ultimately obtaining high-purity copper sulfate crystals. The waste sulfuric acid detection data in Table 1 reveals that the waste sulfuric acid predominantly contains 2.93% of readily oxidizable substances and trace metal ion impurities, meeting the criteria for the production of electroplating-grade copper sulfate. Table 1.Impurity content in waste sulfuric acid.
3.RESULTS AND DISCUSSION3.1Impurity content in waste sulfuric acidThe impurity content in waste sulfuric acid was shown in Table 1. 3.2Polysulfide content in waste sulfuric acidThe mass-to-charge ratio spectrum of standard solution was shown in Figure 2. Figure 2.Mass-to-charge ratio spectrum of standard solution. (a): (NH4)2SO4; (b): Na2S2O3; (c): KHS2O8; (d): K2S2O7; (e): electronic grade sulfuric acid; (f): waste sulfuric acid.  It is known that the sulfuric acid content is about 62.3% (mass fraction), which is about 6.23% after dilution 10 times. Based on the ratio, the polysulfide mass fraction can be calculated as follows: From the analysis of the data measured by the quadrupole time-of-flight mass spectrometer, it was found that the HSO3-, S2O62-, and S2O72- contents in 68% of the waste sulfuric acid were 1.586%, 2.156%, and 1.106% respectively. 3.3Targeted conversion of polysulfides in waste sulfuric acid3.3.1Polysulfide conversion experiment in waste sulfuric acid was shown in Figure 3.In the experiment, DSA serves as the anode, while a stainless-steel plate functions as the cathode. The applied current density is 350 A/m2, and electrolysis is conducted on a 200 mL waste sulfuric acid sample for a duration of 10 min. Figure 3.Mass-to-charge ratio spectra of waste sulfuric acid before and after electrolysis. (a): before electrolysis; (b): after electrolysis.  Following the electrocatalytic oxidation of the waste sulfuric acid solution, the concentrations of HSO3-, S2O62-, and S2O72- in the solution decreased from 1.586%, 2.156%, and 1.106% to 0.017%, 0.011%, and 0.225%, respectively. Then, the data before and after the conversion of polysulfides in electronic-grade sulfuric acid was shown in Table 2. Table 2.Data before and after the conversion of polysulfides in electronic-grade sulfuric acid.
3.2.2Transformation rules of polysulfides in waste sulfuric acid.The experiment was conducted at room temperature, utilizing a Pt electrode as the working electrode, a Ti electrode as the counter electrode, and mercurous sulfate as the reference electrode. The sulfuric acid solution utilized was a sample of electronic-grade sulfuric acid (68%). For experimental purposes, 1.586% sodium sulfite and 1.106% sodium pyrosulfate were separately added to the solution, and measurements of LSV and CV were conducted. Figure 4 depicts the CV curves of sodium sulfite and sodium pyrosulfate in electronic-grade sulfuric acid. Notably, the CV curves of 68% H2SO4 and 68% H2SO4+1.106% Na2S2O7 are essentially identical. A broad oxidation current peak and current plateau are observed in the oxidation zone spanning 0.5 V to 1.2 V, along with a reduction current peak and current plateau in the reduction zone ranging from 0.4 V to 0.8 V. 68%H2SO4+2.4% Na2SO3 exhibits two oxidation peaks at -0.75 V and 0.1 V, corresponding to SO3 2- oxidation and oxygen evolution peaks, respectively. Additionally, an oxidation peak emerges at 0.45 V, speculated to be indicative of a hydrogen evolution reaction7-12. Based on the aforementioned analysis, it is deduced that the predominant reactions occurring in waste sulfuric acid are illustrated in Figure 5. 3.4Copper sulfate analysisAnalyze the CuSO4·5H2O prepared in the previous sections. Additionally, employ ICP-MS for the detection of metal ions in the copper sulfate. Table 3 reveals that the compositions of copper oxide synthesis methods 1 and 2, as well as the associated metal impurity contents, align with the specifications for high-quality copper sulfate for electroplating, with metal impurity contents ≤0.0001 ppm. However, the electrochemical synthesis method exhibits superior quality with lower metal impurity content compared to the chemical synthesis method, enabling the direct synthesis of the fundamental electroplating solution13-15. Table 3.High purity copper sulfate quality standards.
4.CONCLUSIONWaste sulfuric acid generated in the semiconductor industry features low metal ion content but high polysulfide content. The synthesis of copper sulfate results in the formation of polysulfates, influencing the formulation of electroplating solutions and the subsequent deposition of metal copper. This study initially focuses on converting polysulfides in waste sulfuric acid into sulfuric acid and subsequently synthesizing copper sulfate to obtain electroplating-grade copper sulfate. These processes introduce novel ideas and methods for the high-quality utilization of waste sulfuric acid. The experiment employs analytical techniques such as ICP-MS, TOC instrument, quadrupole time-of-flight mass spectrometer, etc., to analyze waste sulfuric acid. The primary impurities in waste electronic-grade sulfuric acid include 0.03% hydrogen peroxide, trace metal ions (<100 ppb), and 4.848% polysulfide. Its purity surpasses that of reagent-grade sulfuric acid. To harness waste sulfuric acid for the production of high-purity, high-quality copper sulfate, the electrocatalytic oxidation method is employed for the targeted conversion of polysulfides in waste electronic-grade sulfuric acid. This process aims to reduce the polysulfide content from 4.848% to 0.284%, thereby mitigating the impact of polysulfides on coatings during copper sulfate. This article conducts a comparative analysis of two technical approaches for producing high-purity copper sulfate: chemical synthesis and electrochemical methods. The investigation reveals that both the copper oxide synthesis method and the electrochemical preparation method yield high-purity sulfuric acid. However, the electrochemical preparation method results in copper sulfate with superior purity, devoid of the introduction of any new impurities during the process. ACKNOWLEDGMENTSThis work was supported by the National Natural Science Foundation of China (No. U1802255) and the National Key R&D Program of China (2019YFC1905802). REFERENCESYang, L., Hu, S. and Gong, H.,
“Development status and prospect of wet electronic chemicals in China,”
Fine and Specialty Chemicals, 31
(11), 1
–9
(2023). Google Scholar
Zhang, B., Qiu, Z., Zhong, H., Mu, J.,
“Preparation and characterization of expanded graphite/modified n-alkanes composite phase change material for drilling in hydrate reservoir,”
Chemical Engineering Journal, 429
(1), 132422
(2022). https://doi.org/10.1016/j.cej.2021.132422 Google Scholar
Gromov, P. B., Kasikov, A. G., Shchelokova, E. A. and Petrova, A. M.,
“Regeneration of sulfuric acid from electrolyte waste of the copper-smelting plant using solvent extraction,”
Hydrometallurgy, 175 187
–192
(2018). https://doi.org/10.1016/j.hydromet.2017.11.008 Google Scholar
Işildar, A., Rene, E. R., van Hullebusch, E. D. and Lens, P. N. L.,
“Electronic waste as a secondary source of critical metals: Management and recovery technologies,”
Resources, Conservation and Recycling, 135 296
–312
(2018). https://doi.org/10.1016/j.resconrec.2017.07.031 Google Scholar
Arshadi, M., Yaghmaei, S. and Esmaeili, A.,
“Evaluating the optimal digestion method and value distribution of precious metals from different waste printed circuit boards,”
Journal of Material Cycles and Waste Management, 22
(4), 1690
–1698
(2020). https://doi.org/10.1007/s10163-020-01043-0 Google Scholar
Zhang, T. and Zhang, L.,
“Recovery and utilization of sulfuric acid from waste acid solution in copper smelting process,”
Copper Engineering, 662 44
–45
(2018). Google Scholar
Chen, G., Chen, S., Zhen, C., Zhou, Z. and Sun, S.,
“Adsorption and oxidation of ethanol on Pt and Sb, S modified Pt electrodes using cyclic voltammetry and EQCM,”
Acta Chimica Sinica, 59
(8), 1253
(2001). Google Scholar
Chen, G., Chen, S., Lin, H., Zheng, X. and Sun, S.,
“Adsorption and oxidation of methanol on pt and sb, s modified pt electrodes using cyclic voltammetry and EQCM,”
Journal of Electrochemistry, 7
(4), 452
–458
(2001). https://doi.org/10.61558/2993-074X.1438 Google Scholar
Schlussel, S. and Kwon, S.,
“A review of formic acid decomposition routes on transition metals for its potential use as a liquid H2 carrier,”
Korean Journal of Chemical Engineering, 39
(11), 2883
–2895
(2022). https://doi.org/10.1007/s11814-022-1276-z Google Scholar
Ike, I. A., Linden, K. G., Orbell, J. D. and Duke, M.,
“Critical review of the science and sustainability of persulphate advanced oxidation processes,”
Chemical Engineering Journal, 338 651
–669
(2018). https://doi.org/10.1016/j.cej.2018.01.034 Google Scholar
Tan, C., Gao, N., Deng, Y., Li, L., Deng, J. and Zhou, S.,
“Kinetic oxidation of antipyrine in heat-activated persulfate,”
Desalination and Water Treatment, 53
(1), 263
–271
(2015). https://doi.org/10.1080/19443994.2013.848414 Google Scholar
Chen, W. S. and Huang, C. P.,
“Mineralization of aniline in aqueous solution by electrochemical activation of persulfate,”
Chemosphere, 125 175
–181
(2015). https://doi.org/10.1016/j.chemosphere.2014.12.053 Google Scholar
Liu, Y., Brogan, L. J., Rigsby, M. A., Huie, M. M., Opocensky, E. C., Spurlin, T. A. and Reid, J. D.,
“Superconformal Copper Electroplating on an Ultrathin Cobalt Seed in an Acidic Copper Sulfate Electrolyte,”
J. Electrochem. Soc., 169
(8), 082508
(2022). https://doi.org/10.1149/1945-7111/ac862d Google Scholar
Li, Q., Hu, J., Zhang, J., Yang, P., Hu, Y. and An, M.,
“Screening of electroplating additive for improving throwing power of copper pyrophosphate bath via molecular dynamics simulation,”
Chemical Physics Letters, 757 137848
(2020). https://doi.org/10.1016/j.cplett.2020.137848 Google Scholar
Noma, H., Koga, T., Hirakawa, C., Nonaka, K., Shobu, K., Kaibuki, T. and Moriyama, S.,
“Analysis of Cu(I) Complexes in Copper Sulfate Electroplating Solution by Using Reaction Kinetics with a Chelate Reagent,”
ECS Trans, 58 77
(2014). https://doi.org/10.1149/05817.0077ecst Google Scholar
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