Metrics details Waste generated during asbestos manufacturing contains substantial quantities of iron The existing techniques for processing chrysotile-asbestos waste (CAW) cannot fully recover these elements Therefore this paper presents a hydrometallurgical method for processing the CAW of the Zhitikara deposit in the Kostanay region of Kazakhstan Batch reactors are used in both laboratory and pilot experiments and initial trials are conducted in a recently constructed industrial Ti reactor at the Kostanay Minerals JSC plant in the Kostanay region of Zhitikara The primary benefits of the industrial reactor include operation without excessively grinding the feedstock and creation of a pulp with enhanced filtration properties A moderate agitation speed (10 rpm) helps ensure a consistent pulp density and prevent the production of silica gel Optimal leaching conditions are determined as a fraction size of CAW between − 1.25 and 0.25 mm An investigation of the process kinetics reveals that diffusion is the rate-controlling step the activation energies are determined to be 54.4 kJ.mol− 1 Washing and recycling water enhances helps to increase the recovery of magnesium chloride Implementing pilot-scale hydrometallurgical processing of CAW can effectively address environmental issues that pose a threat to human health and provide commercial advantages Chrysotile is the only type of sheet silicate whereas the rest are classified within the amphibole subgroup The “Kostanay Minerals” JSC plant was established in 1965 and it is the sole mining company in Kazakhstan and Central Asia that focuses on extracting chrysotile asbestos and producing chrysotile fibers This firm is the leading producer and distributor of chrysotile asbestos globally The asbestos-cement industry is the largest consumer of commercial chrysotile asbestos This industry utilizes asbestos to manufacture roofing sheets which exhibits a well-developed crystalline structure with a suboptimal raw material processing efficiency attributed to the irreversible loss of important components such as magnesium Comparing the two methods revealed that the sulfuric acid treatment in Kazakhstan suffers from a low consumption of magnesium sulfate whereas nitric acid treatment results in solutions with high concentrations of hard-to-recover calcium This paper presents a novel five-stage chemical treatment method for converting CAW into four commercially viable non-toxic products The treatment includes the use of hydrochloric acid and is conducted at the Kostanay Minerals JSC plant Unlike previous studies that focused on the laboratory-scale processing of chrysotile asbestos our study utilized a new pilot batch reactor The suggested treatment procedure is distinguished by optimal conditions (~ 85–90 °C P = 1 atm) and the recurrent utilization of wash water A low stirring speed prevented the formation of silica gel and the reuse of wash fluids significantly enhanced the manufacturing process The solution and solid products acquired during the experiment were evaluated using X-ray diffraction (XRD) The waste generated after serpentinite enrichment was supplied by the Kostanay Minerals JSC plant Kazakhstan) was used as the solvent for experiments 37%) and magnesium oxide (MgO) were purchased from Sigma-Aldrich (USA) The flocculant Praestol 2500 (Ashland Inc. All reagents used were of GR grade (purity ≥ 99%) and all experiments were conducted using deionized water Initial serpentinite and products of serpentinite enrichment: (a) the original serpentinite; (b) asbestos fibers; (c) waste fraction −1.25 + 0.25 mm PSD SEM image of original CAW after magnetic separation. X-ray diffraction pattern of original CAW sample after magnetic separation (non-magnetic fraction). X-ray diffraction pattern of original CAW sample after magnetic separation (magnetic fraction). Particle size distribution histogram of initial material before leaching (a) Laboratory reactor for LSB-HAL experiments; (b) kinematic scheme of the laboratory reactor. Leach liquor (100 mL) is transferred from a storage tank to a reactor using a pump to initiate the first purification process for removing Fe2+ ions. The process of converting Fe2+ to Fe3+ is achieved by introducing hydrogen peroxide and magnesium oxide at a pH range of 4–4.5 and a temperature range of 70–80 °C for a duration of 30 min. The iron (III) hydroxide settles completely within 10–15 min following the addition of magnesium oxide, when the pH is between 7.5 and 8. The precipitation of iron (III) hydroxide occurred in two stages: Scheme of 4-stage countercurrent washing of silica cake Thermodynamic characteristics of the leaching process of chrysotile asbestos technogenic waste from the hydrolytic cleaning of solutions were calculated (Appendix E) The calculations were performed using the HSC Chemistry 5.0 thermodynamic calculation program A 0.5% weight solution of Praestol 2500 was employed to enhance the segregation of the iron-rich cake the purified solution was transferred to a designated storage tank The leached iron-rich cake was washed in three stages using distilled water The water obtained after washing the iron-rich cake was used for pulp preparation and subsequent purification from Ni2+ ions to enhance the recovery of magnesium chloride The precipitation of nickel(II) hydroxide is described by The separation of cakes rich in Fe and Ni was achieved using decantation The transparent liquid that had no color was subjected to heating at a temperature of 105 °C and kept at this temperature to create a bischofite solution (MgCl2 6H2O) with a density of 1.31 g⋅cm–3 The solution contained less than 0.05 g⋅L–1 of Fe3+ and less than 0.005 g⋅L–1 of Ni2+ the prepared solution was transferred into a polypropylene container and dispatched to consumers in accordance with GOST 7759-73 - Magnesium chloride technical (bischofite) The magnesium extraction rates were calculated as follows: P0 – the mass of magnesium in initial material They can function at a temperature of 100 °C and at atmospheric pressure The system was equipped with a detachable cover and vent to allow the release of excess air the device does not generate a centrifugal force This results in the excessive grinding of silicates the separation of the liquid and solid phases becomes challenging The agitation process was conducted using specialized blades that were inserted into the reactor operating at a speed of 10 rpm to ensure a consistent pulp density The reactor was subjected to the simultaneous mixing of the components and leaching The center of gravity in the industrial reactor was situated below the rotational axis of the device the mixing components on the inner surface raised the slurry from the lower layers and elevated the solid particles the particles descended because of the force of gravity positively affecting the blending procedure during leaching The primary benefit of this reactor is its capacity to elevate the slurry from the lower layers to the upper layers using a minimal number of rotations while transporting solid particles at a slower speed than a leaching device with a stirrer This process enabled the production of a slurry with enhanced filtration properties and boosted the filtration speed of silicate-containing materials The results of the PSB-HAL experiments could be reproduced a 100 kg sample of the non-magnetic fraction was placed in an industrial reactor 300 L of an 18 wt% hydrochloric acid solution was heated to a temperature of 85–90 °C for ~ 2 h The solid–liquid ratio of the solution ranged from 1 to 3 The filtrate was obtained with a concentration of 85.5–91.6 g⋅L–1 of Mg2+ and 8–8.5 g⋅L–1 of Fe2+/3+ The filtering rate used was 12 m3∙m− 2 h− 1 The liquid remaining after the SiO2-rich cake washing was utilized for creating a leaching solution and pulp whereas those of Fe and Ni were 87.8% and 81.3% Titanium reactor front (a) and back (b) view for PSB-HAL experiments and kinematic scheme of the reactor (c) The SEM images were obtained using a TESCANVEGA 3 scanning electron microscope equipped with an INCA SDD X-MAX energy-dispersive microanalyzer attachment (Oxford Instruments) and INCA Energy software to plot X-ray spectral microanalysis The XRD patterns of non-magnetic fraction samples were obtained using a DRON-3 diffractometer operating at 35 kV and 20 mA with β-filtered Cu Кα radiation at intervals 0.02o; a step time of 2 s per interval was used The XRD patterns of the magnetic fraction sample were investigated in the two-theta range of 10–80° at a step size of 0.05 using a Bruker D8 Advance diffractometer with Cu-Ka source at 40 kV and 40 mA The phases were identified using the International Diffraction Data file ICDD 2020 and analyzed using PCPDFWIN and EVA programs with a PDF-2 diffraction database The specific surface area of ​​solids (m2 g− 1) was determined using a SORBTOMETR-M device and the micropore volumes (Vmic) of the samples were calculated from their isotherms The particle size was detected using a Sieve Analyzer 30 (Vibrotechnik LLC The particle size distribution of the chosen fraction at each leaching step was analyzed by photo images using the image processing package of the Fiji Image J software The chemical composition of the serpentinite waste of fraction − 1.25 + 0.25 mm after enrichment and before magnetic separation was determined through atomic absorption spectroscopy (Agilent AA-240 The silicon content of the samples were determined using the gravimetric method and Cr) and chlorine concentrations in the liquors and solids were determined via atomic absorption spectrophotometry (Agilent 240 AA Model Ferrous and magnesium ions concentrations were determined in the liquors by standard redox titration with trilon B (C10H14N2Na2O8·2H2O) Previous studies focused on the laboratory-scale production of magnesium chloride from serpentinite9 whereas iron and nickel were solely removed by hydrolytic purification of the solutions The recovery of Fe and Ni was not estimated although the overall magnesium extraction rate reached 92% This research aimed to improve the efficiency of the established hydrometallurgical method and rate at which silica This paper presents a hydrometallurgical process for CAW that comprises five steps: The original CAW was separated from the iron-bearing minerals using magnetic separation The non-magnetic fraction was leached with hydrochloric acid and the resulting silica-rich cake was recovered The solution was evaporated and the bischofite was recovered The general dissolution reaction is represented by Eqs. (7–12) A hydrochloric acid concentration of 18% was used for treatment at an S/L ratio of ~ 1/3 w/v This study investigated the effect of HCl consumption on the leaching process in a laboratory reactor. The experiment focused on an acid consumption range of 80–120% of the stoichiometry, as indicated in Table 2 The extraction of Mg and its concentration from the solution also increase with an increase in the consumption of HCl the concentration of acid remaining in the productive solution increases thereby necessitating the use of a substantial amount of neutralizers during the hydrolytic purification process for removing contaminants Optimal outcomes were attained when the acid consumption reached 100% stoichiometry The efficiency of the magnesium extraction was 95% with a concentration of 76.8 g⋅L–1 in the productive solution and S/L ratio were maintained at 18 wt% HCl the CAW particles remain suspended in the liquid without settling at the bottom The leaching efficiency of Mg was enhanced from 11 to 98% by increasing the agitation rate from 20 to 300 rpm thereby resulting in an increase in the concentration of Mg2+ in the solution from 10 to 93.8 g⋅L–1 a substantial decrease in the filtration rate was observed when the agitation speed was increased to 300 rpm These findings indicate that particles break and produce silica gel when a stirrer is used at high speeds in a beaker thereby resulting in the inability to separate the solid phase The lower stratum of the reacting solids is subjected to pressure from a suitably elevated layer of reacting solids when employing a vertical laboratory reactor which leads to the disintegration and excessive pulverization of the feed material Substantially decreasing the height of the reacting column is necessary to reduce excessive grinding of the feed material which can lead to gelation and decreased filtration rates Leaching process in a chemical beaker: (a) at 100 rpm; (b) at 300 rpm. (a) The effect of agitation speed on the magnesium leaching in the lab reactor; the particle size distribution of samples (b) after 1st leaching; (c) after 2nd leaching at 10 rpm in the laboratory reactor The mechanical activation used for rocks with Σ(Mg Ca)/Si ratio values is lower than 1.28 (ideal serpentinite) Ca)/Si result suggests that CAW is a less complex rock because it has a higher value (1.38) than that of ideal serpentinite Decreasing the particle size increases the degree of decomposition with an increase in the contact surface the pulp filtration process becomes impaired by the transfer of SiO2 into the solution a less intensive mechanical activation can be applied to CAW to reduce the cost of the process More intensive mechanical activation is not required to increase the leaching efficiency and this reduces the energy consumption of the pretreatment method and enables the use of dilute acids mechanical activation applied to CAW to reduce its size to 0.25–2.0 mm increased Mg2+ recovery up to 94.5% the filtration rate deteriorates because of the gelation process from 0.33 to 0.04 m3⋅m− 2⋅h− 1 Praestol 2500 increased the filtration rate by 3–5 times A horizontal rotating batch reactor was used for processing the technogenic waste The main advantage of this reactor is that the pulp lifts from the lower layers at a low rotation number moving particles of the solid material at a speed lower than that in a laboratory reactor with an agitator The agitation speed of the stirrer was reduced from 20 to 300 rpm (in the laboratory beaker, Table 4) to 10 rpm (in the laboratory reactor, Table 5) to reduce the over-grinding of the original CAW A solid phase was maintained in the suspension under these conditions Similar filtration rates were observed for fractions − 2 + 1.25 mm which can be explained by the formation of silica gel and deterioration of the filtration characteristics of the pulp a horizontal laboratory reactor with a low agitation speed of 10 rpm demonstrated high Mg2+ recovery The experimental data for successive four-stage countercurrent washing cycles in a laboratory reactor and washing water circulation after CAW leaching are listed in Table 6 The magnesium amount in the productive solution decreased to 11.4 and 3.8 g⋅L–1 following the first and fourth washing cycles Approximately 95.7% of magnesium (91.9 g⋅L–1 Mg2+) was successfully extracted from the cake The recovery of Mg2+ decreased to 4.8% and 1.9% when the density of the solution decreased from 1.079 to 1.005 g cm3 The pH value increased from 0.50 to 2.64 because of the neutralization caused by the addition of a suspension of MgO The recycling of washing water reduced costs and enabled the recovery of up to 96% of magnesium chloride in the technological process The greatest degree of magnesium extraction is 19% at a temperature of 25 °C increasing the temperature to 85 °C allows for nearly total extraction Continuing to raise the temperature to 95 °C does not yield a substantial impact and is not feasible a reaction temperature range of 85–90 °C is selected as the most favorable for the magnesium leaching process Effect of temperature and reaction time on the magnesium leaching in the laboratory reactor (S/L = 1/3; HCl = 100% from stoichiometry, HCl concentration − 18%; ω = 10 rpm). Plot of SCM with time at various temperature (a) diffusion model, (b) chemical reaction model (S/L = 1/3; HCl = 100% from stoichiometry, HCl concentration − 18%; ω = 10 rpm). Arrhenius plot for the leaching process (S/L = 1/3; HCl = 100% from stoichiometry The CAW (210 kg) were separated into magnetic (35 kg) and nonmagnetic (175 kg) fractions 309 kg of 37% hydrochloric acid (CAW/HCl ratio ~ 1:3 w/v) heated at 85–90 °C for ~ 2 h was poured into the reactor The resulting slurry was cooled to room 20 °C and filtered a green solution of 1 (473 kg) and a siliceous cake (135 kg) were obtained The siliceous cake was subjected to four successive countercurrent water washing cycles The washed SiО2-rich cake was dried at 105 °C to yield 100 kg of a dry solid product (Appendix A) and the obtained Fe-rich cake was washed three times with water (3 ⋅ 100 kg H2O) at an S/L ratio of 1/1 w/v the residue was drained and passed through a suction filter The filtrate was poured into a tank with wash water The resulting washed iron-rich cake weighing 75 kg was dried in a tube furnace at 105 °C (see Appendix D) Washing water was sent for further sedimentation so that the subsequent washing water was fed to the previous washing stage A third washing cycle was performed using clean water The exhaust gases were captured and neutralized in the gas scrubber through a ventilation system The resulting washed nickel-rich cake weighing 70 kg was dried in a tube furnace at 105 °C (Appendix D) A purified magnesium chloride solution weighing 475 kg (Appendix Bc) was evaporated in a crystallizer at 110 °C to a density of 1.31 g/cm3 and poured into a polypropylene container The proposed stages for PSB-HAL of CAW and bischofite recovery SEM images of siliceous cake after PSB-HAL experiments (first stage of leaching). SEM images of siliceous cake after PSB-HAL experiments (second stage of leaching) the average pore size did not change significantly X-ray diffraction pattern of siliceous cake after first leaching with hydrochloric acid. X-ray diffraction pattern of siliceous cake after the second leaching with hydrochloric acid The primary benefit of the proposed process is the elimination of the logistics expenses associated with imported products These costs form a major portion of the price of the end product because of the relatively cheap cost of goods and the great distances they need to be transported The current potential buyers are Kostanay Minerals JSC and Zhitikara LLP The values were estimated for 2018–2019 and remained stable since then A study on the leaching of CAW samples in an acidic solution by adding hydrogen peroxide as an oxidizing agent for iron and nickel has been reported Leaching was performed in batch laboratory-(V = 2 L) and pilot-scale (V = 1000 L) reactors The results suggest the following conclusions: The optimum leaching conditions were established Water washing and recycling are highly efficient methods for the recovery of magnesium chloride A low agitation speed (10 rpm) during laboratory and industrial acid leaching allows maintaining uniform pulp density and preventing the formation of silica gel A study of the kinetics of this process indicated that diffusion is the rate-controlling step with an activation energy of 54.4 kJ⋅mol–1 and NiO in the CAW were converted into their corresponding chlorides during the chlorination acid treatment A simplified efficiency analysis of the proposed method results showed that the commercial value of the products was cheaper than that of the available analog by 1.6 times The pilot-scale hydrometallurgical processing of CAW confirmed their potential commercial applicability in practice the bischofite solution (MgCl2⋅6H2O) with a density of 1.31 g cm− 3 have been used for carnallite production both at the laboratory and industrial scale at Kostanay Minerals JSC (Zhitikara deposit Amorphous silica can be used as a filler in the rubber industry to produce paints All sub-products can find applications in building material production as pigments (Fe-rich cake) and in nickel production (Ni-rich cake) This method was feasible for extracting Mg and Ni from CAW with relatively low production energy and cost providing useful information for the future development and utilization of CAW All data generated or analyzed during this study are included in this published article and its supplementary information files In case of any queries or requirement of data please contact the corresponding author (A.A evaluation of asbestos hazard in ophiolitic rock mélanges a case study from the Ligurian Alps (Italy) Hazardous minerals mining: challenges and solutions Managing asbestos waste using technological alternatives to approved deep burial landfill methods: An Australian perspective Serpentine minerals; structures and petrology Guidelines for geologic investigations of naturally occurring asbestos in California Contrasting chemical compositions in associated lizardite and chrysotile in veins from Elba Complex processing of wastes generated in chrysotile asbestos production Clear and simple detection of asbestos stained with two dyes for building materials collected from disaster and demolition sites using a stereomicroscope Quantitative analysis of asbestos-containing materials using various test methods Method of complex processing of ore containing magnesium silicates Method of manufacturing magnesium from oxide-chloride stock Method for producing magnesium from silicon-containing waste Method for complex processing of magnesium silicates Impact of pulp rheological behavior on selective separation of Ni minerals from fibrous serpentine ores Magnesium extraction from asbestos mine tailings: a report Magnola technology for magnesium production. 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Kinetics of leaching: a review. 38 113–148. https://doi.org/10.1515/revce-2019-0073 (2022) Download references The authors gratefully acknowledge financial support from project “253-17GK Organization of bischofite production from chrysotile asbestos technogenic raw materials” of the Ministry of Education and Science of the Republic of Kazakhstan Republican State Enterprise National Center for Complex Processing of Mineral Raw Materials of the Republic of Kazakhstan Writing – Original Draft.Mukhametzhanova A.: Investigation Writing – Original Draft.Akbayeva D.: Formal analysis Writing – Review & Editing.Terlikbaeva Validation.Alimzhanova A.: Formal analysis The authors declare no competing interests Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations Below is the link to the electronic supplementary material Download citation DOI: https://doi.org/10.1038/s41598-024-83239-0 Anyone you share the following link with will be able to read this content: a shareable link is not currently available for this article Sign up for the Nature Briefing newsletter — what matters in science