HCl Concentration Research Articles

Nano MNO2 production from fine-grained and low-grade manganese ore using a mixture of citric acid and molasses as reductant

ABSTRACT This study was carried out to investigate the production of manganese nanomaterials by enriching fine-grained and low-grade manganese ores. Ore was taken from Balıkesir region in Turkey. Experimental studies were discussed in two different stages. In the first stage, the ore was enriched by a leaching method and optimum enrichment conditions were determined. For this, different mixtures of acids and reducing agents were used. The optimum Mn dissolution was 120 minutes. 97.05% Mn dissolution efficiency was obtained from the ore containing 29% MnO under a 120 minute leaching time, 600 rpm stirring speed, 2 M HCl and HNO3 (3:1) concentration, 0.5 M citric acid + 10% molasses reducers and at 90 °C. In the second stage, the Mn solution dissolved under optimum conditions was photo-reduced by exposure to sunlight and then MnCO3 was produced using Na2CO3. The produced MnCO3 was roasted and 200 nm MnO2 nanorods were obtained.

Extraction of pure Co, Ni, Mn, and Fe compounds from spent Li-ion batteries by reductive leaching and combined oxidative precipitation in chloride media

The redox equilibria – also taking chloro–complexation into account – and the thermodynamics of the HCl – Co – Ni – Mn system have been examined. The leaching efficiencies of the LiCoO2 (LCO), LiNiMnCoO2 (NMC111), and LiFePO4 (LFP) black masses were studied in the 1 – 10 M HCl concentration and the 25 – 95 °C temperature ranges. A minimum of 2 M HCl concentration with an 80-minute contact time at 95 °C was sufficient to achieve > 98 % leaching yields from the LCO material. By increasing the HCl concentration to 6 M, the leaching time could be halved. The NMC cathode material could even be leached completely at 80 °C with 2, 4, 8, and 10 M HCl in 50, 40, 10, and 8 min, respectively. The same yield could be achieved even at only 25 °C using 6, 8, and 10 M HCl for ∼ 310, 125, and 50 min, respectively. A relation was found between the chloride ion activity and the leaching yields, while the evolution of Cl2 was also examined to help explain leaching kinetics. The purity of the graphite residue reached 99.9 % (referring to Co, Ni, Mn, Li) after two cross-current leaching steps. The oxidative precipitation – using hypochlorite solutions - partially generated by utilizing the Cl2 from leaching - was examined in the 1–6 pH range showing that selectivity significantly increases with decreasing pH, but the degree of reagent utilization also decreases. Kinetic factors were also pointed out to markedly affect selectivity. The combined hydrolytic–oxidative precipitation process could recover 96–98 % pure raw oxides, which were further refined to 98–99.8 % purity by scrubbing in acidic MnSO4 and CoSO4 solutions.

Investigation of corrosion behavior of 2205 duplex stainless steel coiled tubing in complex operation environments of oil and gas wells

In this paper, the corrosion behavior of 2205 duplex stainless steel coiled tubing in acidizing and production environments was studied by high-temperature and high-pressure corrosion weight loss tests, stress corrosion cracking test, electrochemical tests, microscopic morphological analysis and corrosion product analysis. The results show that in the acidizing environment, the duplex stainless steel has high corrosion rates especially in the acidizing solution with high HCl concentration, with the selective dissolution of ferrite phase. In the production environment containing CO2 and H2S, the duplex stainless steel has excellent resistances to corrosion and stress corrosion cracking. With the increase of pH value, the pitting potential and polarization resistance exhibit the increasing trend, indicating the better passivation performance. Therefore, 2205 duplex stainless steel coiled tubing can be recommended to be mainly used for the operations in production environment rather than acidizing operations.

Efficient removal behaviors and correlation rules of Na from Zhundong coal with low concentration organic acids

The effects on the removal of Na from Zhundong coal were investigated systemically using ten organic acids including seven aliphatic saturated acids and three aromatic acids as well as two inorganic acids of low concentration. The results show that the structure and concentration of acids, leaching temperature and time are the main factors influencing Na removal from coal. The removal rate of Na, if only deionized water (DI) is used for leaching, is 52.03% resulting from water-soluble inorganic Na. When the acid concentration is 0.01 mol/L, the removal rate of total Na can reach 88.67–99.18% for aliphatic saturated acids, 85.26–89.38% for aromatic acids and 99.28–99.35% for HCl and H2SO4, indicating that the most organic Na can be removed by ion exchange between H+ and Na+ except for water-soluble inorganic Na. The removal amount of both total Na and organic Na increases basically linear with the increase of inorganic or organic acids until nearly the highest removal amount for different acids. The theoretical removal amount of Na and the optimum acid addition can be quantitatively calculated based on the correlation rules between the Na removal and the different acids, for example, ytotal Na(mmol/g) = 0.39xacid(mmol/g) + 0.099 for acetic acid (AA) and ytotal Na(mmol/g) = 0.56xacid(mmol/g) + 0.097 for HCl. The removal differences for various organic acids are mainly due to the difference in acidity and the molecular structure of organic acids. The Na2O content in coal ash decreases greatly from 6.21% for raw coal and 2.77% for water leaching coal to 0.22–0.95% for low concentration organic acids treated coal and ca. 0.21% for low concentration HCl and H2SO4 treated coal.

Pretreatment optimisation of Ulva spp. for production of bioH2 and lactic acid as added-value product

This study compares hydrothermal and diluted acid-thermal pretreatments at 100 °C for hydrolysate production from Ulva spp. Aiming at bioH2 production at 55 °C. Three extractants were evaluated in hydrothermal pretreatment: distilled water (H-DW), natural (H-NS) and synthetic seawater (H-SS). The HCl concentration (N), the Ulva spp. Percentage (% w/v), and hydrolysis time (h) in diluted acid-thermal pretreatment were optimised using a central composite design and a desirability function to maximise the total carbohydrate concentration and yield while minimising the HMF and furfural concentration. The hydrolysate from hydrothermal pretreatments, depending on the pretreatment time and %Ulva, achieved bioH2 production from 20 to 47% lower than the optimised diluted acid-thermal pretreatment (0.3 N HCl, 35%Ulva, and 2.5 h), which was 66.83 (±3.89) NmL gglucose−1. The hydrolysate also indicates potential for lactic acid (HLa) production, resulting in 1.47 molHLa molglucose−1, before being consumed after 1.6 days and contributing to the bioH2 production.

Efficient utilization of red mud waste via stepwise leaching to obtain α-hematite and mesoporous γ-alumina

Utilizing the red mud sustainably is now a challenging issue. Red mud due to its wide production, presence of some radioactive elements, high alkalinity, and salinity, has a dramatic potential to contaminate soil and groundwater. Notwithstanding its drawbacks, Red mud consists several elements, including Ca, Al, Ti, Si, and Fe, in various mineral forms. In this study, stepwise leaching was applied as a proper method to separate and purify the main valuable elements using available and affordable HCl. The pre-leaching step under optimized conditions using HCl (0.2 M) at room temperature for 2 h removed 89% of the calcium content from red mud. To selectively remove the solid silica, the residue was treated with concentrated HCl (3.0 M, L/S of 20 mL/g) at 95 °C, resulting in the dissolution of iron and aluminum content with up to 90% efficiency. After precipitation of the Fe3+ and Al3+, they were characterized using FT-IR, BET, EDS, XRD, SEM and TEM monographs, confirming the formation of nanosized hematite (α-Fe2O3) and mesoporous gamma alumina (γ-Al2O3). Consequently, inexpensive red mud was converted into highly valuable nano-sized metal oxides using simple, sustainable techniques and cheap reagents. Moreover, this technique generates the lowest amounts of waste during the leaching process and all reagents can be recycled for further uses, making this method a sustainable utilization.

Hardness and corrosion behaviour of stir cast LM26 Al/sugar palm fibre ash composites

PurposeThe conflicting results on the corrosion characteristics of aluminium matrix composites reinforced with agrarian waste have stimulated an investigation on the hardness and corrosion rate of sugar palm fibre ash (SPFA) reinforced LM26 Al/alloy composite by varying the SPFA from 0 to 10 wt% in an interval of 2 wt%. This paper aims to discuss the aforementioned issue.Design/methodology/approachThe composites were produced via stir-casting and the hardness was determined using a Vickers hardness testing machine, corrosion rate was examined through the weight loss method by immersion in 0.5, 1.0 and 1.5 M hydrochloric acid (HCl) at temperatures of 303, 318, and 333 K for the maximum duration of 120 h. The morphological study was conducted using a scanning electron microscope (SEM) on the samples before and after immersion in HCl.FindingsThe incorporation of SPFA improved the hardness of the alloy from 58.22 to 93.62 VH after 10 wt% addition. The corrosion rate increases with increased content of SPFA, the concentration of HCl and temperature. The least corrosion rate of 0.0272 mpy was observed for the LM26 Al alloy in 0.5 M after 24 h while the highest corrosion rate of 0.8511 mpy was recorded for LM26 Al/10 wt% SPFA in 1.5 M HCl acid after 120 h. The SEM image of corroded samples revealed an increased number of pits with increased SPFA content.Research limitations/implicationsThe work is limited to SPFA up to 10 wt% as reinforcement in LM26 Al alloy, the use of HCl as corrosion medium, temperatures in the range of 303–333 K, and a weight loss method were used to evaluate the corrosion rate.Originality/valueThe corrosion rate was determined for LM26 Al/SPFA composites with various amounts of SPFA in 0.5, 1.0 and 1.5 M HCl at 303, 318 and 333 K and compared with the matrix alloy.

Leaching Efficiency and Kinetics of Platinum from Spent Proton Exchange Membrane Fuel Cells by H2O2/HCl

The increasing carbon emissions from various fossil fuels have led to the search for efficient and clean energy sources to replace them. Proton exchange membrane fuel cells (PEMFCs) are a promising alternative, but the use of platinum as a catalyst material poses challenges due to its limited resources and low abundance. This study proposes an efficient method for platinum recovery while retaining spent membranes. The membrane and catalyst were separated using isopropanol, and the spent membrane was dissolved in a 50% ethanol solution to prepare the precursor for subsequent membrane regeneration. Hydrochloric acid (HCl) was used as the leaching agent, and the experimental parameters such as HCl concentration, H2O2 concentration, contact time, and operating temperature were optimized to achieve the highest platinum leaching rate. Finally, through isothermal leaching experiments, the leaching mechanism was investigated using the shrinking core model, indicating the involvement of both surface chemical and inner diffusion mechanisms in the platinum leaching process, primarily controlled by the inner diffusion mechanism. Under optimal conditions, the platinum leaching rate was about 90%, and the activation energy of the reaction was calculated to be 6.89 kJ/mol using the Arrhenius equation.

Treatment of steel industry wastewater by Poly-Aluminum-Ferric-Silicate coagulant prepared from coal gasification ash

The coal gasification industry generates a large amount of coal gasification ash (CGA) which can contaminate environment by seeping harmful substances into both soil and water. In this study, CGA was used for the preparation of Poly-Aluminum-Ferric-Silicate coagulant (PAFSiC) to treat steel industry wastewater, and the effects of acid leaching, alkaline leaching, and copolymerization stages were investigated. Our results indicated that the dissolution rates of iron and aluminum from CGA were 53.49% and 55.43%, respectively, under leaching temperature at 95 °C, time at 1.4 h, and concentration of HCl at 5.1 mol/L. The dissolution rate of silicon from the residue of CGA leaching by HCl was 41.44% under leaching temperature at 75 °C, time at 0.5 h, and concentration of NaOH at 5 mol/L. The PAFSiC prepared under (Fe+Al)/Si molar ratio at 4.3 indicated the best coagulation performance, and its removal rates for turbidity, color, and chemical oxygen demand (COD) from steel industry wastewater were 93.69%, 36.47%, and 62.66%, respectively. Compared to commercial polysilicate aluminum ferric (PSAF), PAFSiC increased removal rates of for turbidity, color, and COD by 28.67%, 18.21%, and 7.38%, respectively. The coagulation efficiency of PAFSiC was influenced by pH; a removal rate of color of 54.43% was recorded from the steel industry wastewater using PAFSiC prepared at pH of 2. PAFSiC synthesized from CGA under (Fe+Al)/Si molar ratio at 4.3 exhibited a branching amorphous structure with spatial stereoscopic sense, resulting in higher capacity to bind with and remove contaminates. Our results underline the potent performance of PAFSiC as a viable solution to alleviate pollution from the steel industry.

Recovery of rare earth elements from phosphogypsum using subcritical water extraction

Phosphogypsum (PG) is generated in massive amount in the production of fertilizer. It has been indicated that PG is a promising secondary source for rare earth elements (REEs). This study examined the leaching of REEs, including yttrium (Y), lanthanum (La), cerium (Ce) and neodymium (Nd) from PG utilizing subcritical water extraction (SWE). Hydrochloric acid (HCl) was selected as the leaching reagent, and the leaching efficiency increased with increasing HCl concentration and decreasing solid to liquid ratio (S/L). Complete leaching of REEs (100.36% of Y, 97.50% of La, 100.06% of Ce and 96.58% of Nd) was achieved under experimental conditions of 0.1 mol/L HCl, 10 g/L, 100 °C, initial pressure of 10 kg/cm2, and 5 min. The total energy consumption in SWE was 4.2 × 106 kJ/kg. Leaching efficiency of Y, La, and Nd slightly increased as temperature increased to 125 °C, and decreased when further increased to 150 °C. The behavior was due to solubility of anhydrite as affected by temperature and pressure under subcritical conditions, and the enhanced mass transfer. From comparisons, SWE could be an efficient and green technology for the recovery of REEs from PG.

Influence of HCl concentration in source solution and growth temperature on formation of α-Ga2O3 film via mist-CVD process

We have examined the effect of synthesis conditions on α-Ga2O3 film, one of the ultra-wide bandgap semiconductors, on c-plane sapphire substrate via mist CVD process. The resultant film is dominantly composed of α-Ga2O3 phase, but a small amount of κ-Ga2O3 phase coexists when the growth temperature is higher. The source solution containing higher concentration of HCl expands the range of temperatures at which single-phase α-Ga2O3 is grown and suppresses the inclusion of κ-Ga2O3 at higher growth temperatures. Moreover, the growth with higher concentration of HCl up to 0.66 mol l−1 increases the growth rate and improves the surface roughness. Thus, HCl has a crucial role in the selective growth of α-Ga2O3 and the quality of the film. Also, some pits are observed at the surface of α-Ga2O3 and κ-Ga2O3 is precipitated inside the pit defect when the concentration of HCl is low and the growth temperature is high.

Arang Kulit Biji Kakao (Theobroma cacao L) sebagai Adsorben untuk Menurunkan Kadar Asam Lemak Bebas pada Pembuatan Biodiesel dari Minyak Jelantah

Indonesia as one of the largest producing and exporting countries of crude palm oil (CPO). However, Indonesia still has not utilized the potential of the waste that generated by using CPO as cooking oil, namely used cooking oil. The high content of free fatty acids (FFA) in used cooking oil will cause the saponification reaction and interfere the processing into biodiesel. Cocoa bean shell charcoal (Theobroma cacao L) has a K2CO3 content similar to its commercial product, and contains some traces of silicates and sulfates so that it can increase the efficiency of reducing free fatty acids. In this study, tests were carried out to reduce FFA levels in used cooking oil using charcoal from cocoa bean husks activated with HCl, varying the concentrations of 6, 8 and 10 Molar, as well as the temperature treatment during the process of mixing used cooking oil with activated charcoal adsorbent, which was 75 , 100, and 150°C. The best FFA reduction results were found in the A3T2 reactor which reached 80%, where the best HCl concentration was 10 Molar and the temperature of the mixing process with the adsorbent was 100°C and produced a biodiesel yield of 75%. The quality of the biodiesel produced complies with SNI 7182-2015 standards, 867 kg/m3 of density, 0.5 mg KOH/g of acid number, 1.52 cSt of kinematic viscosity, 48.081 MJ/kg of calorivic value and 143.99%- mass of methyl ester content.

Experimental Investigation on Physicochemical and Wetting Characteristics of Modified Gas Coal: Effects of Multicomponent Acids and Surfactant

Abstract In this study, the effects of the different concentrations of hydrochloric acid, hydrofluoric acid, and acetic acid and a surfactant on the physicochemical characteristics of coal, such as pore diameter distribution, pore fractal dimension, and chemical structures were studied. The wettability performance of the reagent-modified coal was proposed. The results demonstrated that the mineral dissolution rate of HF in the coal sample was much higher than those by HCl and HAC treatment, which increases the surface roughness of coal. With the increase in the concentration of a multicomponent acid solution, the number of micropores decreased and the number of macropores increased. Moreover, both fractal dimensions D1 and D2 of the coal sample treated with the multicomponent acid comprising 6% HCl, 6% HF, and 6% HAC (#3) were the smallest. This shows that compound reagent #3 is available to enhance the pore size distribution with a better effect than the other five ones. Compared with the raw coal (#7), treatment with high concentrations of HCl (#4) significantly decreased the contact angle on coal (#4), whereas treatment with high concentrations of HF or HAC (#6 or #5), significantly increased it.

Experimental optimization of physicochemical factors for spontaneous deposition of 210Po using newly designed deposition kit

A simple spontaneous deposition kit for 210Po determination using alpha spectrometry was newly designed, and polonium deposition characteristics under various physicochemical conditions were evaluated using it. The high-purity silver disc (99.99%) showed high deposition efficiencies of over 85.1% in the HCl concentration range of 0.01–6 M. Optimal physicochemical factors were determined to be a temperature of 90 °C, deposition time of 90 min, and the use of ascorbic acid as a reducing agent in an amount similar to that of the interfering element (Fe).

Hydrogel Preparation from Shrimp Shell-Based Chitosan: The Degree of Crosslinking and Swelling Study

Chitosan is a natural polymer derived from different starting materials such as fish scales, crab and shrimp shells. Due to the advantages like biocompatibility and biodegradability, chitosan has been widely used in hydrogel development. This current study aims to make chitosan from shrimp shells, synthesize hydrogel from chitosan, and observe the effect of various chitosan preparation treatments on the properties of the hydrogel. The preparation of chitosan was carried out through demineralization, deproteinization, and deacetylation process. HCl concentration during demineralization and NaOH concentration during deproteinization were varied (1; 1,5; 2) M and (1; 1,5; 2) M, respectively. Chitin deacetylation was conducted using 60% (w/v) of NaOH at the temperature of 90oC for 120 min, and chitosan was resulted. Chitosan based hydrogel was then synthesized with the addition of alginate and glutaraldehyde. The effect of HCl and NaOH concentrations during demineralization and deproteinization on the deacetylation degree of chitosan was observed. The effect of deacetylation degree of chitosan on the degree of crosslinking and swelling property of the hydrogel were also evaluated. Chitosan resulted from this study has the optimum degree of deacetylation at 57.28 %, resulting from demineralization by using HCl 2M and deproteinization with NaOH2 M. Higher deacetilation degree of chitosan causing the increase of the degree of cross-linking and decrease of the swelling capacity of the hydrogel. The highest degree of cross-linking is 78.85 %, and the swelling capacity is 47 %.

Significant enhancement of photocatalytic activity of g-C3N4/vermiculite composite by the introduction of nitrogen defects

Nitrogen-defect g-C3N4/vermiculite composites (gCVx, x = 0.1, 1, 3, 4) with high efficient photocatalytic performance were constructed by a wet chemical method cooperating with the calcination process, as well as using the pre-expanded vermiculite and the melamine pre-treated by hydrochloric acid solutions of 0.1, 1, 3, 4 mol/L, respectively. Micron-sized g-C3N4 sheets with nitrogen defects were synthesized and uniformly distributed in the gCVx composites. Photocatalytic performance was evaluated by degrading Rhodamine B (RhB) aqueous solution. The results indicated that photocatalytic activities of gCVx increased firstly and then dropped down gradually with the increase of HCl concentration. gCV3 achieved the maximum degradation rate of 97.90 % for RhB after photocatalysis for 20 min, whose degradation rate constant was 14.9 times than that of bulk g-C3N4. gCV3 also exhibited the highest photocatalytic activity toward degrading the tetracycline and phenol solutions. The excellent photocatalytic performance was ascribed to the enhanced amounts of active sites, increased specific surface area, improved visible light absorption ability, accelerated charge transfer and separation efficiency of photogenerated-carriers, which resulted from the synergistic effect between vermiculite and nitrogen defects in g-C3N4, as well as the mutual electrostatic repulsion between the negative-charged vermiculite and the photo-induced electron from the nitrogen-defect g-C3N4.

SCREENING OF FUNGI FROM THE TRICHOCOMACEAE FAMILY (ASPERGILLI AND PENICILLIA) IN PRODUCTION OF HEXOSE SUGARS FROM AGRO-WASTE

As an alternative to crude oil, the production of hexose sugars from agro-waste may be viewed as an environmentally benign process for sustainable chemicals/fuels production. A range of high-value industrial chemicals and fuels can be accessed from biomass-derived hexose sugars. This work evaluated the production of hexose sugars from yam peels (agro-waste) via enzymatic hydrolysis using different fungi from the trichocomaceae family namely, Aspergillus niger, Aspergillus tamari, Pencillium citrinum, and Penicillium chrysogenum respectively. The agro-waste (yam peels) samples were inoculated directly with the respective fungi without any form of pre-treatment. Hexose yields of 8.75±0.07%, 8.10±0.07%, 2.75±0.25% and 2.75±0.25 were obtained for A. niger, A. tamari, P. citrinum, and P. chrysogenum respectively when the samples were sterilized for 20 minutes at 121oC. Under the same experimental conditions, the control sample gave a minimal yield of 1.50±0.35%. Regardless of the enzyme employed, the amount of hexose sugars produced increased steadily with an increase in sterilization time (40, 60, 80, and 100 minutes). Optimum hexose yields of 16.90±0.71%, 15.50±0.35%, 7.00±0.01%, 7.00±0.05% were recorded for A. niger, A. tamari, P. citrinum, and P. chrysogenum respectively at 100 minutes sterilization time. Generally, P. citrinum, and P. chrysogenum gave similar but low hexose yields while A.niger and A. tamari afforded high and distinct hexose yields. Amongst the different fungi screened, A. niger was the most efficient enzyme for the hydrolysis giving the highest hexose sugar yields under the different conditions employed. The performance of the different fungi was evaluated against three different concentrations (0.5M, 1.0 M, 1.5M) of HCl and H2SO4 acid-catalysed hydrolysis of the yam peels respectively. At 1.0 M concentrations HCl and H2SO4 respectively, the hexose yields of 6.40 ± 0.40 % and 7.60 ± 0.20% obtained were on par with those obtained for the enzymes P. citrinum (7.00±0.01%) and P. chrysogenum (7.00±0.05%) after 100 minutes sterilization time. Regardless of acid concentrations, A. niger, and A. tamari enzymes were more effective for the hydrolysis than the HCl and H2SO4 acid-catalysed process with A. niger being the most effective for the hydrolysis. Therefore, a combination of the A-niger and any heterogenous green catalyst is a promising strategy for further transformation of hexose sugars obtained from agro-wastes to higher value chemicals like levulinic acid in a one-pot synthesis. The extended sterilization time may also be a suitable pre-treatment alternative to mineral acids.

Estonian Phosphate Rock Dissolution in Hydrochloric Acid: Optimization of Acid Dosage and Concentration

The increasing need for phosphorus and rare earth elements (REEs) has initiated the studies of new mineral deposits and new complex processing technologies. Estonian phosphate rock (EPR) resources, which are not in use, are estimated to be more than 3 billion metric tons or 800 million tons of P2O5. The experiments of dissolution of three different EPR samples in hydrochloric acid were carried out with the aim of studying the impact of the chemical and mineralogical composition of EPR on the leaching process. The leaching of P, Ca, Mg, and consumption of H+ ions depend on HCl concentration and dosage. The solubility of fluorine and REEs are also influenced by CaF2 and REEs-phosphates precipitation. Fe solubility depends on the mineralogical composition of EPR but also on particle size, acid dosage, pH, and phosphorus content in the solution. The dissolution of pyrite is much lower than the solubility of carbonate apatite. Dolomite dissolution depends on the acid dosage and the fractional composition of EPR. Dolomite dissolution also rests lower than that of apatite. For all the samples studied, the best regression models that describe P, Mg, and Ca solubility and the optimum concentration of HCl for phosphorus dissolution were found using mathematical modeling.

ВЛИЯНИЕ ТЕХНОЛОГИЧЕСКИХ ПАРАМЕТРОВ СОЛЯНОКИСЛОТНОГО РАЗЛОЖЕНИЯ НЕФЕЛИНА НА ФИЛЬТРУЕМОСТЬ КРЕМНЕЗЕМНЫХ ОСТАТКОВ

The results of studies on the influence of technological parameters (temperature, HCl concentration, etc.) on the separation rate of the liquid and solid phases of the reaction pulp from the hydrochloric acid decomposition of nepheline are presented. Based on the data obtained, optimal decomposition conditions were selected, under which the highest filtration rate was achieved: acid concentration 25–30 %; process temperature 85–95 °C; duration of loading nepheline into acid 3.03.5 hours with an additional exposure of 0.51 hour and the consumption of "seed" 1015 % of the mass of nepheline.

Migration and Conversion of Phosphorus in Hydrothermal Carbonization of Municipal Sludge with Hydrochloric Acid

Phosphate ore is a non-renewable resource, so finding a replacement is necessary. Municipal sludge has significant recycling potential because of its high phosphorus content and large discharge characteristics. The migration and transformation of phosphorus in municipal sludge treated with different concentrations of HCl were studied using the standards, measurements, and testing phosphorus extraction protocol from two aspects: phosphorus complexation and mineral form. After the hydrothermal carbonization treatment without HCl, the hydrochar retained 99.7% of phosphorus in the sludge, and the organophosphorus percentage was about 30%. In the hydrothermal carbonization treatment with the addition of 0.5–2.5% HCl, the phosphorus content in the hydrochar decreased gradually from 99.5% (46.18 mg/g) to 91.8% (64.17 mg/g) that of the original sludge, and the proportion of non-apatite inorganic phosphorus increased from 34% to 94%. Hydrochloric acid provides a low-pH environment and promotes the dissolution of calcium-related phosphorus precipitates and enhances the dehydration reaction. This study provides technical support for the recovery of phosphorus resources from municipal sludge.