Optimal Pretreatment Conditions Research Articles

Impact of Hulling and Heat Treatment on the Physicochemical Properties, Bioactivity and Bioavailability of Iron and Zinc of the G196 Soybean Variety Produced in Burkina Faso

This study delved into the impact of hulling and two types of heat treatment on the physicochemical, bioactive properties and bioavailability of the G196 soybean produced in Burkina, in order to not only find the optimal conditions for pre-treatment of seed, but also to guide their use in food formulations. Standard analytical methods were used for physicochemical and biochemical analyses. The results showed an increase in ash content by 0.04% as a result of seed shelling, while steaming led to a significant decrease in ash with a reduction rate by 0.06%; 0.08%; 0.25% after 20min, 40min and one hour, respectively. An average increase in total dry materials by 0.03% and reduction in moisture by 6.33% were observed after one hour of roasting. Additionally, shelling and steaming increased total carbohydrate contents. Roasting and steaming caused a significant reduction in protein, but an increase was observed after hulling. Carbohydrate levels decreased over the course of three roasting times. Regarding bioavailability, the zinc content improved after 40 minutes of roasting. Shelling also reduced the phytate content by 11.89%, while steaming significantly reduced the phytate, resulting in a drop in the phytate content by 17.18%; 18.02% and 19.71% after twenty, forty minutes and one hour, respectively. A significant reduction in phytate content by 26.64% after 40 minutes, and 46.46% after one hour was observed during heat treatment by roasting.

Ultrasound and enzymatic treatments to improve protein extraction from cress seeds, and the characterization of protein isolates

In this study, proteins were extracted from cress seeds using enzymatic pretreatment and ultrasound. Optimization of enzymatic pretreatment, employing a multi-enzyme complex rich in carbohydrases, aimed to maximize extraction yield and reduce sugar content. Ultrasound replaced classical extraction under optimal conditions by comparing functional properties between enzyme-treated and untreated samples. Combined enzymatic pretreatment and ultrasound significantly increased extraction yield from 39.56% to 94.03%. Optimal enzymatic pretreatment conditions included pH 3.84, 45.16 °C, enzyme concentration 2.32 FBGU/g seed, and 3.71 h of treatment time. Ultrasound-treated isolates exhibited superior functionality and minimal structural changes, with molecular weights ranging from ∼22 kDa to ∼59 kDa. These findings underscore the potential of cress seed protein isolate for diverse applications, enhanced through enzymatic pretreatment and ultrasound, owing to its high nutritional quality.

Facilitating the fabrication of diverse bio-based nanomaterials from bamboo using one-pot hydrated deep eutectic solvent pretreatment

The conversion of biomass feedstocks into bio-based nanomaterials was made easier with hydrated DES (HDES) pretreatment, which can boost the value-added applications of lignocellulosic biomass. In this study, two types of HDESs were initially prepared by 3-Chloro-2-hydroxypropyltrimethyl ammonium chloride (CHPTAC) with formic acid (FA) and acetic acid (AA), respectively. We achieved rapid conversion of bamboo feedstock into bio-based nanomaterials (including lignin nanoparticles, LNPs; lignin-containing cellulose nanofibers, LCNFs) through one-pot microwave-assisted HDES pretreatment coupled with robust nanofabrication strategies. The findings demonstrated that an impressive delignification ratio of 92.10 % and a cellulose retention ratio of 92.95 % were achieved under the optimal DES pretreatment conditions (120 °C, 20 min). The fractionated lignin fractions were effortlessly self-assembled into dispersed, uniformly shaped circular LNPs (<100 nm) using a novel proposed strategy, which was successfully applied to stabilizing oil-in-water (O/W) Pickering emulsions. To produce LCNFs, we conducted functionalization of cellulose-rich residue in aqueous citric acid followed by simple ultrasonic treatment. Compared to the control LCNF, the LCNF-based self-assembly films exhibited significantly improved mechanical properties and hydrophobicity (water contact angle 106.26°). In short, the proposed HDES pretreatment combined with robust nanofabrication strategies will broaden the fractionation and fabrication of bio-based nanomaterials, enhancing their potential in promising fields.

Higher efficiency of vanadate iron in heterogeneous Fenton-like systems to pretreat sugarcane bagasse and its enzymatic saccharification.

Pretreatment is crucial for effective enzymatic saccharification of lignocellulose such as sugarcane bagasse (SCB). In the present study, SCB was pretreated with five kinds of heterogeneous Fenton-like systems (HFSs), respectively, in which α-FeOOH, α-Fe2O3, Fe3O4, and FeS2 worked as four traditional heterogeneous Fenton-like catalysts (HFCs), while FeVO4 worked as a novel HFC. The enzymatic reducing sugar conversion rate was then compared among SCB after different heterogeneous Fenton-like pretreatments (HFPs), and the optimal HFS and pretreatment conditions were determined. The mechanism underlying the difference in saccharification efficiency was elucidated by analyzing the composition and morphology of SCB. Moreover, the ion dissolution characteristics, variation of pH and Eh values, H2O2 and hydroxyl radical (·OH) concentration of FeVO4 and α-Fe2O3 HFSs were compared. The results revealed that the sugar conversion rate of SCB pretreated with FeVO4 HFS reached up to 58.25%, which was obviously higher than that under other HFPs. In addition, the surface morphology and composition of the pretreated SCB with FeVO4 HFS were more conducive to enzymatic saccharification. Compared with α-Fe2O3, FeVO4 could utilize H2O2 more efficiently, since the dissolved Fe3+ and V5+ can both react with H2O2 to produce more ·OH, resulting in a higher hemicellulose and lignin removal rate and a higher enzymatic sugar conversion rate. It can be concluded that FeVO4 HFP is a promising approach for lignocellulose pretreatment.

Enhanced anaerobic co-digestion of cattle manure with food waste and pig manure: Statistical optimization of pretreatment condition and substrate mixture ratio

This study investigated the optimal pretreatment condition and mixture ratio of cattle manure (CM) for its efficient anaerobic co-digestion (AcoD) with food waste (FW) and pig manure (PM). The pretreatment performances of thermal (TM), microwave (MW), and ultrasound (US) technologies and the AcoD performance were statistically and experimentally evaluated at various mixture ratios of CM, FW, and PM. The results revealed that the most effective pretreatment condition with the TM, MW, and US pretreatments was 129.3 °C for 49.6 min, 824.2 W for 7.3 min, and 418.0 W for 36.3 min, respectively. The best AcoD performance of optimally pretreated CM (PCM) was achieved when 30.5 % PCM was mixed with 42.5 % FW and 27.0 % PM. A long-term evaluation showed that the start-up rate for the anaerobic mono-digestion of PCM was 2.3 times faster than that of CM and the amount of methane produced was 4.7 times higher; process stability was thus preferentially maintained under a higher organic loading rate (OLR) (2.0 kg-VS/m3∙d). The start-up rate for the AcoD of PCM with FW and PM was 1.2 times higher than that of the AcoD of CM with FW and PM. Although the performance gap between the AcoD reactors after steady state was not significantly different, the PCM AcoD reactor provided a more stable operation under a higher OLR (5.0 kg-VS/m3∙d). This study demonstrates that the pretreatment and co-digestion of CM could significantly enhance the production of biogas and improve process stability.

Selective Removal of Hemicellulose by Diluted Sulfuric Acid Assisted by Aluminum Sulfate.

Hemicellulose can be selectively removed by acid pretreatment. In this study, selective removal of hemicellulose was achieved using dilute sulfuric acid assisted by aluminum sulfate pretreatment. The optimal pretreatment conditions were 160 °C, 1.5 wt% aluminum sulfate, 0.7 wt% dilute sulfuric acid, and 40 min. A component analysis showed that the removal rate of hemicellulose and lignin reached 98.05% and 9.01%, respectively, which indicated that hemicellulose was removed with high selectivity by dilute sulfuric acid assisted by aluminum sulfate pretreatment. Structural characterizations (SEM, FTIR, BET, TGA, and XRD) showed that pretreatment changed the roughness, crystallinity, pore size, and functional groups of corn straw, which was beneficial to improve the efficiency of enzymatic hydrolysis. This study provides a new approach for the high-selectivity separation of hemicellulose, thereby offering novel insights for its subsequent high-value utilization.

Enhanced adsorption of dye wastewater by low-temperature combined NaOH/urea pretreated hydrochar: Fabrication, performance, and mechanism.

The highly stable biomass structure formed by cellulose, hemicellulose, and lignin results in incomplete conversion and carbonization under hydrothermal conditions. In this study, pretreated corn straw hydrochar (PCS-HC) was prepared using a low-temperature alkali/urea combination pretreatment method. The Massloss rateof cellulose, hemicellulose, and lignin from pretreated biomass, as well as the effects of the pretreatment method on the physicochemical properties of PCS-HC and the adsorption performance of PCS-HC for alkaline dyes (rhodamine B and methylene blue), were investigated. The results showed that the low-temperature NaOH/urea pretreatment effectively disrupted the stable structure formed by cellulose, hemicellulose, and lignin. NaOH played a dominant role in solubilizing cellulose and the combination of low temperature and urea enhanced the ability of NaOH to remove cellulose, hemicellulose, and lignin. Compared to the untreated hydrochar, PCS-HC exhibited a rougher surface, a more abundant pore structure, and a larger specific surface area. The unpretreated hydrochar exhibited an adsorption capacity of 64.8% for rhodamine B and 66.32% for methylene blue. However, the removal of rhodamine B and methylene blue by PCS-BC increased to 89.12% and 90.71%, respectively, under the optimal pretreatment conditions. The PCS-HC exhibited a favorable adsorption capacity within the pH range of 6-9. However, the presence of co-existing anions such as Cl-, SO42-, CO32-, and NO3- hindered the adsorption capacity of PCS-HC. Among these anions, CO32- exhibited the highest level of inhibition. Chemisorption, including complexation, electrostatic attraction, and hydrogen bonding, were the primary mechanism for dye adsorption by PCS-HC. This study provides an efficient method for utilizing agricultural waste and treating dye wastewater.

Efficient bio-hydrogen production by dark co-fermentation of food-rich municipal solid waste and urban pruning wastes of pine, cypress, and berry

Bio-hydrogen (bio-H2) production from dark co-fermentation of pruning wastes, from pine, cypress, and berry trees, and food-rich municipal solid waste (FMSW) was evaluated as a promising way to combine waste management and renewable energy production. The inoculum was initially optimized by heat-shock pretreatment at 65, 75, 85, and 95 ℃ for 15, 30, and 45 min to maximize bio-H2 yields. The optimum pretreatment conditions (75 °C for 45 min) were applied for dark co-fermentation analyses. The highest bio-H2 production yield of 84 ± 6 mL/g VS was obtained by dark co-fermentation of 20 g/L pruning wastes and FMSW under initially neutral conditions. The fermentation of individual substrates led to 40.9, 0.2, 0.1, and 0.2 mL/g VS from FMSW, pine, berry, and cypress, respectively, 85% lower than that obtained through dark co-fermentation. Therefore, co-processing of a “stiff substrate”, lignocellulose, with a “loose part”, starchy FMSW, leads to a higher bio-H2 yield. Dark co-fermentation led to the bio-conversion of more than 76% of starch, 31% of glucan, and 41% of hemicellulose, besides 41% lignin removal. The modified Gompertz model (MGM) and Logistic model (MLM) were well-fitted on kinetic data (with R2 values ≥0.98), and the kinetic parameters were calculated.

Grade identification of rice eating quality via a novel flow-injection voltammetric electronic tongue combined with SFFS-BO-SVM

Given the importance and complexity of grade identification for rice eating quality, this study aimed to use a self-established flow-injection voltammetric electronic tongue (FIE-tongue) combined with SFFS-BO-SVM to replace human sensory evaluation. A novel FIE-tongue was firstly designed and established in this work, and the optimal rice pretreatment conditions were determined by fractional factorial design (FFD) which used for FIE-tongue detection. Based on optimized detection data, the optimized features and hyperparameters of 16 samples in three eating quality grades for SVM model were obtained by Sequential Floating Forward Selection (SFFS) algorithm and Bayesian Optimization (BO) algorithm, respectively. Compared to the original SVM model established by all features, the accuracy of SFFS-BO-SVM model for different grades were all higher than 92%, and have the increasement of 5.5%, 18.8%, and 11.4%, respectively. Therefore, the FIE-tongue combined with SFFS-BO-SVM method should be promising for rice eating quality grading and other food quality control.

Advancing safe bioenergy production from cadmium-contaminated sweet sorghum through mild synergistic pretreatment

Phytoremediation is an eco-friendly and cost-effective method for treating cadmium (Cd)-contaminated soil. However, safe disposal of harvested hyperaccumulators remains scarce. Herein, a mild synergistic pretreatment combining dilute acid and alkali pretreatment was developed for safe biorefining of the Cd-containing sweet sorghum, and Cd was centrally extracted into the acid pretreatment liquid in the first step. The results showed that the synergistic pretreatment was more effective in removing Cd from the biomass and overcoming biomass recalcitrance. During the synergistic pretreatment, the Cd concentration in biomass dramatically decreased from 4.03 to 0.00626 mg/kg, and a considerable amount of lignin and hemicelluloses in biomass was removed, facilitating enzymatic saccharification and safe bioenergy production. The optimal conditions of the synergistic pretreatment resulted in a total sugar yield of 81.6 wt %, which was 4.7-fold higher than that of the original biomass. This strategy holds promise for reducing the cost of industrial saccharification and is a valuable inspiration for the safe handling and resource utilization of Cd-containing biomass.

Protein hydrolysates prepared by Alcalase using ultrasound and microwave pretreated almond meal and their characterization.

The study aimed to optimize ultrasonic (US: 40kHz/200W for 10, 20, 30, 40, and 50min), and microwave (MW: 160W for 45, 90, 125, 180, and 225s) pretreatment conditions on protein extraction yield and degree of protein hydrolysis (DH) from almond de-oiled meal, an industrial by-product. First order model was used to describe the kinetics of almond protein hydrolysates obtained with Alcalase. The highest DH, 10.95% was recorded for the US-50min and 8.87% for MW-45s; while it was 5.76% for the untreated/control sample. At these optimized pretreatment conditions, a 1.16- and 1.18-fold increment in protein recovery was observed for theUS and MW pretreatments, respectively in comparison to the conventional alkaline extraction. The molecular weight distribution recorded for pretreated samples disclosed a significant reduction in the band thickness in comparison with control. Both the pretreatments resulted in a significant increase (P < 0.05) in the antioxidant activity, and TCA solubility index when compared with the control. Results evinced that US and/or MW pretreatments before enzymatic hydrolysis can be a promising approach for the valorization of almond meal for its subsequent useas an ingredient for functional foods/nutraceuticals which otherwise fetches low value as an animal feed.

Combining thermal–alkaline hydrolysis pretreatment with catalytic supercritical water gasification for hydrogen production from sewage sludge

An integrated process consisting of a thermal–alkaline hydrolysis pretreatment (TAHP) combined with catalytic supercritical water gasification (CSCWG) was developed to treat sewage sludge to produce H2. TAHP facilitated the transfer of organics from sludge into liquid products for subsequent CSCWG to produce H2. Upon increasing the hydrolysis temperature, time, and alkali dosage, the continuous transfer of organics to liquid products was observed, wherein the hydrolysis temperature had the greatest effect. Under the optimal pretreatment conditions (180 °C, 1 h, and mNaOH/mOM = 25 %), approximately 70 % of proteins, carbohydrates, and 50 % of humus in sludge, i.e., easily gasified organic species, were transferred. Using this process, the TOC concentration in the liquid products reached about 17,000 mg/L, and the polysaccharide and soluble protein concentrations reached 2400 and 15,000 mg/L, respectively. With this integrated process, the H2 yield and selectivity increased by 3.7–7.6 times and 5.94–52.92 times, respectively, compared with the directly catalyzed gasification of sludge. This improvement occurred because TAHP promoted the transfer of easily gasified organic species into the liquid products, while the difficult-to-gasify organics and inorganics in ash remained in the solid phase, which prevented them from inhibiting the catalyst.

Optimized Solid–Liquid Separation of Phenolics from Lavender Waste and Properties of the Dried Extracts

Lavender distillation produces huge quantities of solid waste yearly. This waste is usually discarded, resulting in serious environmental issues. However, it still contains residual essential oil and other bioactive compounds. This research reports on the development and comparison of optimized solid–liquid separation methods, i.e., microwave- (MAE) and ultrasound-assisted extraction (UAE) of phenolic compounds from lavender distillation waste. The optimal pretreatment conditions, such as waste moisture content and particle size, were also determined. The extracts were spray- or freeze-dried and the resulting powders were characterized for their physicochemical properties. The majority of the original phenolic compounds in lavender were found in the leachate fraction after distillation (61%), whereas 43% was found in the solid waste. Drying of the solid waste before extraction affected the process efficiency. UAE led to a higher phenolic content and greater antioxidant properties compared to MAE. Drying (spray or freeze) the extracts did not significantly affect their phenolic content, whereas the use of maltodextrin as a drying agent improved the drying process yield, especially when using the freeze-drying method. It is concluded that valorization of lavender distillation wastes can be achieved via an integrated process consisting of a green extraction method and a consequent drying process that results in a stable bioactive powder.

Efficient hemicellulose removal from lignocellulose by induced electric field-aided dilute acid pretreatment

This study evaluated the effectiveness of induced electric field (IEF) as a novel electrotechnology to assist dilute acid pretreatment of wheat straw (WS) at atmospheric pressure and low temperature (90 °C). The effects of acid concentration and duration on cellulose recovery, hemicellulose and lignin removal were investigated. Meanwhile, the differences between IEF pretreatment and hydrothermal pretreatment were compared by quantitative and qualitative analysis. The optimal pretreatment condition was acid concentration 1 % with the period of 5 h. Under the parameters, the hemicellulose removal of WS after IEF pretreatment was up to 73.6 %, and the enzymatic efficiency was 55.8 %. In addition, the irregular surface morphology, diminished functional groups associated with hemicellulose, increased specific surface area and pore volume, as well as improved thermal stability of the residual WS support the remarkable effect of IEF pretreatment. The feasibility of IEF pretreatment is might be due to the fact that the magneto-induced electric field promotes ionization of H+ and formation of hydrated hydrogen ions, increasing the acidity of the medium. Secondly, electroporation disrupts the anti-degradation structure of WS and increases the accessibility of cellulose to cellulases. It indicated that IEF is a green and efficient strategy for assisting the separation of hemicellulose from lignocellulose.

1-Ethyl-3-methylimidazolium acetate pretreatment for maximizing reducing sugar recovery from mixed cabbage residue.

Vegetable waste, including mixed cabbage residue (MCR), is considered a promising raw material for bioenergy production because of its high lignocellulosic component. In this study, the pretreatment of MCR by ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) was optimized based on response surface methodology. The optimal condition for MCR pretreatment was determined at 55.8°C, with a reaction of 2.65h and liquid-solid ratio of 4.60:1 v/w. Hydrolysis of pretreated MCR from optimal pretreatment conditions generated a maximum glucose yield of 156.65 ± 7.66mg/g MCR. Untreated and pretreated MCRs were successfully characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The pretreated MCR exhibited increased clear pores and incomplete structure. Moreover, compared with untreated biomass, decreased lignin, decreased hemicellulose, increased surface area, and cellulose crystallinity were observed. Thus, [Emim][OAc] pretreatment is a promising alternative approach for higher glucose production from MCR.

Low-background interference detection of glyphosate, glufosinate, and AMPA in foods using UPLC-MS/MS without derivatization.

The abuse of herbicides has emerged as a great threat to food security. Herein, a low-background interference detection method based on UPLC-MS was developed for the simultaneous determination of glufosinate, glyphosate, and its metabolite aminomethylphosphonic acid (AMPA) in foods. Initially, this study proposed a simple and rapid pretreatment method, utilizing water extraction and PRiME HLB purification to isolate glyphosate, glufosinate, and AMPA from food samples. After the optimization of pretreatment conditions, the processed samples are then analyzed directly by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS) without pre-column derivatization. The method can effectively reduce interference from by-products of pre-column derivatization and background substrates of food sample, showing low matrix effects (ME) ranging from - 24.83 to 32.10%. Subsequently, the method has been validated by 13 kinds of food samples. The recoveries of the three herbicides in the food samples range from 84.2 to 115.6%. The limit of detection (LOD) is lower to 0.073mg/kg, 0.017mg/kg, and 0.037mg/kg, respectively. Moreover, the method shows an excellent reproducibility with relative standard deviations (RSD) within 16.9%. Thus, the method can provide high trueness, reproducibility, sensitivity, and interference-free detection to ensure human health safety.

Sustainable vine shoots-to-ethanol valorisation by a sequential acid/organosolv pretreatment

In this study, a fractionation and valorisation scheme for vine shoots is proposed for biofuel and lignin production. This agricultural waste was fractionated by acid/organosolv sequential pretreatment. In the first step, acid pretreatment was optimised at 150ºC and 1.2% H2SO4 to release hemicellulosic sugars, of which 76% could be recovered. This sugar stream was co-fermented by E. coli with an ethanol yield higher than 98% after detoxification with resins or NH4OH. The solid obtained under optimal acid pretreatment conditions was delignified by organosolv treatment, and a delignification rate of 43% was reached at 180ºC. This substrate with 83% enzymatic digestibility was bio-converted into ethanol by simultaneous saccharification and fermentation, with a yield of 76%. Additionally, lignin was recovered from the organosolv liquor, aiming for the full valorisation of the biomass, which showed a syringyl/guaiacyl ratio of 0.92 by nuclear magnetic resonance, complying with the data provided for Fourier transform infrared spectroscopy and confirming the aromaticity of this fraction for further valorisation.

Pretreatment and enzymatic hydrolysis optimization of lignocellulosic biomass for ethanol, xylitol, and phenylacetylcarbinol co-production using Candida magnoliae.

Cellulosic bioethanol production generally has a higher operating cost due to relatively expensive pretreatment strategies and low efficiency of enzymatic hydrolysis. The production of other high-value chemicals such as xylitol and phenylacetylcarbinol (PAC) is, thus, necessary to offset the cost and promote economic viability. The optimal conditions of diluted sulfuric acid pretreatment under boiling water at 95°C and subsequent enzymatic hydrolysis steps for sugarcane bagasse (SCB), rice straw (RS), and corn cob (CC) were optimized using the response surface methodology via a central composite design to simplify the process on the large-scale production. The optimal pretreatment conditions (diluted sulfuric acid concentration (% w/v), treatment time (min)) for SCB (3.36, 113), RS (3.77, 109), and CC (3.89, 112) and the optimal enzymatic hydrolysis conditions (pretreated solid concentration (% w/v), hydrolysis time (h)) for SCB (12.1, 93), RS (10.9, 61), and CC (12.0, 90) were achieved. CC xylose-rich and CC glucose-rich hydrolysates obtained from the respective optimal condition of pretreatment and enzymatic hydrolysis steps were used for xylitol and ethanol production. The statistically significant highest (p ≤ 0.05) xylitol and ethanol yields were 65% ± 1% and 86% ± 2% using Candida magnoliae TISTR 5664. C. magnoliae could statistically significantly degrade (p ≤ 0.05) the inhibitors previously formed during the pretreatment step, including up to 97% w/w hydroxymethylfurfural, 76% w/w furfural, and completely degraded acetic acid during the xylitol production. This study was the first report using the mixed whole cells harvested from xylitol and ethanol production as a biocatalyst in PAC biotransformation under a two-phase emulsion system (vegetable oil/1M phosphate (Pi) buffer). PAC concentration could be improved by 2-fold compared to a single-phase emulsion system using only 1M Pi buffer.

Production of xylooligosaccharides from different pretreated Camellia oleifera shell with crude enzyme from Aspergillus fumigatus

Production of xylooligosaccharides (XOS) from Camellia oleifera shell (COS) using the crude enzyme from Aspergillus fumigatus (A. fumigatus) was investigated. COS was subjected to different pretreatments, namely thermal autoclaving, combination of diluted acid, diluted alkali or concentrated alkali with thermal autoclaving, microwave-assited ethanol pretreatment. The results showed that the combination of diluted alkali with thermal autoclaving is the best pretreatment for XOS production. The optimal conditions for enzymatic xylooligosaccharides production from the best pretreatment are: temperature 50 °C, pH 4.5, substrate concentration 8% (m/V), enzymatic hydrolysis time 9 h, and enzyme dose of 40 IU/g substrate. A maximum yield of 17.08 ± 0.67 g/L of XOS was obtained under the above optimum conditions for the best pretreatment.

Investigation of the Impact of Electrochemical Hydrochlorination Process Parameters on the Efficiency of Noble (Au, Ag) and Base Metals Leaching from Computer Printed Circuit Boards

The development of environmentally friendly and energy-saving processes for recycling electronic waste (e-waste) is still relevant today. The research presented in this work relates to hydrometallurgy, namely, the electrochemical leaching of metals from e-waste under the action of alternating current (AC) into hydrochloric acid solutions of electrolytes, and can be used for leaching both noble and non-ferrous metals from secondary raw materials. The main object of the study was disintegrator-crushed mixed computer PCBs metal-rich powders with a particle size (d) of &lt;90 µm. The impact of such leaching process parameters as temperature (Tel) and composition of the electrolyte solution, AC density (i) on the electrodes, experiment duration (tex) while maintaining a constant electrolyte temperature (60 °C, 70 °C, and 80 °C) on the metal (Au, Ag, Cu, Al, Ni, Pb, Sn, Ti, Zn, and Fe) leaching efficiency has been studied. In addition, under similar experimental conditions, but without external control of Tel, the kinetics of metal leaching from raw material powders obtained via PCBs single and double crushing in a disintegrator has been also presented. Comparison of raw material powders obtained from different batches of the source material showed both the variability of its chemical composition and the different kinetics of Au and Ag leaching under the same experimental conditions. The optimal conditions for pretreatment of the raw material obtained by single crushing in a disintegrator (CHCl = 6 mol·L−1, i = 0.88 A·cm−2, tex = 1 h, solid-to-liquid ratio—8.6 g·L−1 and without external control of Tel) were determined. It has been shown that this electrochemical pretreatment is accompanied by transition of only base metals into the electrolyte solution, making it possible to significantly reduce their concentration in the final solution. Under pretreatment conditions, the following degree of metal leaching (RMe) has been established: RCu = 98.2%, RAl = 62.8%, RNi = 53.4%, RPb = 93.2%, RSn = 98.0%, RTi = 88.5%, RZn = 61.6%, and RFe = 78.8%. As a result of a subsequent two-hour electrochemical treatment of a solid residue, the degree of leaching of gold and silver was 73.6% and 86.7%, respectively. The presented results provide a broader understanding of the possibility of using the proposed electrochemical hydrochlorination method for noble and base metals leaching from waste PCBs. The novelty and practical value of this research is a validation of the developed technology in laboratory conditions using the real batch of the PCBs. This approach may also be useful to researchers involved in the recycling of other types of secondary raw materials.