Phosphorus recovery from aqueous product of hydrothermal carbonization of cow manure.

The work studies the recovery of nutrients (phosphorus and nitrogen) from the process water of acid-assisted hydrothermal carbonization (HTC) of cow manure. Three organic acids (formic acid, oxalic acid, and citric acid) and sulfuric acid were evaluated as additives in HTC. Using 0.3 M sulfuric acid, more than 99% of phosphorus and 15.6% of nitrogen from manure are extracted and dissolved during HTC at 170 °C with 10 min reaction time in a batch reactor. Nutrients (mainly phosphorus) were recovered through precipitation from process water by raising the ionic strength of the solution by addition of salts of magnesium and ammonia, and by raising the pH to 9.5. Subsequently, phosphorus-rich solids were recovered containing almost all (greater than 95%) of the dissolved phosphorus in the sulfuric and formic acid assisted runs. Morphology and qualitative chemical analysis of the precipitates were determined. It is shown by XRD that the precipitate formed from process water generated by HTC with oxalic acid is crystalline, although the diffraction pattern could not be matched with any expected substance.

High value-added lignin extracts from sugarcane by-products.

This study evaluates the production of lignin bioactive extracts from sugarcane bagasse (SCB) and straw (SCS) alkaline black liquors using greener precipitating agents (methane sulfonic acid (MSA), formic acid (FA) and lactic acid (LA)) as replacers of sulfuric acid (SA), the most common one used in industry. Results showed that the highest precipitation yield was achieved by LA when applied to SCB (14.5 g extract/100 g SCB). Lignin SCB extracts were similar in composition in terms of total carbohydrates (61-70 %), lignin (22-30 %) and inorganics (1.6-2.6 %). Regarding the SCS extracts, similar yields were obtained among all extracts, however, differences in composition were observed between SA and greener precipitating agents, particularly in terms of sugar content. All extracts exhibited radical scavenging activity; overall the extracts were more effective in the scavenging of ABTS radical. FA was the most promising alternative to SA to recover lignin bioactive extracts. This work suggests organic acids as good candidates for obtaining valuable extracts from alkaline pulping of SCB and SCS instead of the conventional sulfuric acid.

Pretreatment with dilute maleic acid enhances the enzymatic digestibility of sugarcane bagasse and oil palm empty fruit bunch fiber.

Lignocellulose is resistant to degradation and requires pretreatment before hydrolytic enzymes can release fermentable sugars. Sulfuric acid has been widely used for biomass pretreatment, but high amount of degradation products usually occurred when using this method. To enhance accessibility to cellulose, we studied the performances of several dilute organic acid pretreatments of sugarcane bagasse and oil palm empty fruit bunch fiber. The results revealed that pretreatment with maleic acid yields the highest xylose and glucose release among other organic acids. The effects of concentration, duration of heating and heating temperature were further studied. Dilute maleic acid 1 % (w/w) pretreatment at 180 °C was the key to its viability as a substitute for sulfuric acid. Moreover, maleic acid did not seem to highly promote the formation of either furfural or 5-HMF in the liquid hydrolysate after pretreatment.

Acid deposition at higher acidity weakens the antagonistic responses during the co-decomposition of two Asteraceae invasive plants.

Co-invasion by two invasive plant species (IPS) can occur in the same habitat. Diversified acid deposition may change the co-invasion process by altering litter decomposition and plant-soil feedback signalling. This study examined the co-decomposition of two Asteraceae IPS (Solidago canadensis L. and Bidens pilosa L.) on litter decomposition rate, soil enzyme activities, and soil N-fixing bacterial communities under diversified acid deposition (mixed acid deposition at pH 5.6 and at pH 4.5, sulfuric acid at pH 4.5, and nitric acid at pH 4.5). B. pilosa litter degraded faster than S. canadensis litter. Acid deposition at higher acidity accelerated the decomposition rate of both pure S. canadensis litter and the equally mixed litters from the two Asteraceae IPS. Antagonistic responses may occur during the co-decomposition of the two Asteraceae IPS with mixed acid deposition, regardless of the pH, as well as with nitric acid deposition at pH 4.5; in contrast, there may be neutral responses for the co-decomposition process with sulfuric acid at pH 4.5. The type of acid deposited may be one of the key factors affecting the intensity of the mixing effect affecting the co-decomposition. Acid deposition at higher acidity weakened the antagonistic responses for the co-decomposition of the two Asteraceae IPS compared with the response to weak acids. Together, these results indicate that acid deposition at higher acidity could facilitate the co-invasion of the two Asteraceae IPS mainly through accelerated litter decomposition as well as weakened antagonistic responses for co-decomposition.

Preparation and structure-activity relationship of highly active black garlic polysaccharides.

The aim of this study was to establish a method to improve the biological activity of polysaccharides. Three acid-treated polysaccharides (BGPS-2, BGPS-3 and BGPS-4) were obtained by treating black garlic polysaccharides (BGPS-1) with sulfuric acid at different intensities. The structure was characterized using the sulfuric acid-carbazole assay, IC, HPSEC-MALLS and FT-IR. The biological functions were evaluated using antioxidant and melanin biosynthesis inhibition assays. Compared with BGPS-1, the molecular weight of acid-treated polysaccharides significantly decreased, and the uronic acid content significantly increased. Antioxidant capacity negatively correlated with molecular weight, whereas melanin inhibition activity positively correlated with uronic acid content. BGPS-4 had the highest antioxidant capacity and the lowest molecular weight (1.25 × 103 Da), 79.41 % lower than that of BGPS-1. BGPS-3 was the strongest inhibitor of melanin formation and had the highest uronic acid content (50.73 %), 238.2 % higher than that of BGPS-1. Molecular weight and uronic acid content were the main structural characteristics that affected the antioxidant and melanin biosynthesis inhibition activities, respectively. BGPS-1, BGPS-2, BGPS-3, and BGPS-4 all had ß-linked pyranose, multi-branched, and non-triple helical spiral structures. Therefore, the acid hydrolysis method markedly modified the structural characteristics of black garlic polysaccharides, and increased their antioxidant capacity and melanin biosynthesis inhibition activity.

Use of Nd:YVO4 laser, photodynamic therapy, sulfuric acid and sand blasting on improving bond integrity of PEEK to resin cement with adhesive.

AIM: The present study aimed to inspect and compare several PEEK surface treatments modifications using Photodynamic therapy (PDT), Neodymium-doped yttrium orthovanadate (Nd:YVO4) laser, Sulphuric acid (H2SO4), and sandblasting (SB) when bonded to composite resin via an adhesive system MATERIAL AND METHODS: One hundred disk-shaped PEEK specimens were prepared by CAD-CAM milling and randomly distributed into five groups based on surface treatment methods: group1: Control (no treatment), group 2: PDT, group 3: Nd:YVO4 laser, group 4: H2SO4 and group 5 sandblasting. Later bonding was pursued using resin cement with an adhesive system. Measurements of surface roughness employing a surface profilometer, water contact angle by the static drop method, SBS by universal Testing machine, and failure modes of de-bonded PEEK specimens by Stereomicroscope were attained. Execution of statistical analysis was performed by two-way analysis of variance ANOVA and Tukey's post hoc test (p>0.05). The Shapiro-Wilk normality test and Bartlett's test for homoscedasticity were also performed. RESULTS: The highest SBS was exhibited by Nd:YVO4 laser (16.33 ± 0.71 MPa) and the lowest SBS was observed in the control group (9.4 ± 1.02). However, PEEK specimen luted with resin cement treated with PDT (16.21 ± 0.14 MPa) and H2SO4 (15.23 ± 0.63 MPa) displayed a comparable SBS to Nd:YVO4 laser (p>0.05). The results of Ra exhibited that PEEK material when exposed to Nd:YVO4 laser (15.252 ± 1.581 µm) unveiled the highest Ra. Nd:YVO4 laser (131.25 ± 2.9 µm) and PDT (130.24 ± 3.7 µm) showed comparable WCA values (p>0.05).Adhesive failure was dominant. CONCLUSION: PEEK surface treated with photodynamic therapy and Neodymium-doped yttrium orthovanadate laser and bonded to composite resin via an adhesive system significantly improved shear bond strength, surface roughness, and water contact angle.

One-step synthesis of garlic peel derived biochar by concentrated sulfuric acid: Enhanced adsorption capacities for Enrofloxacin and interfacial interaction mechanisms.

This study put forward a one-step carbonization method by concentrated sulfuric acid to prepare garlic peel derived biochar, and the synthetic conditions were optimized by L16(45) orthogonal experiments. Notably, in order to study the differences between the proposed synthetic method and the conventional pyrolysis method, the concentrated sulfuric acid carbonized garlic peels biochar (CSGPB) was compared with pyrolysis derived garlic peel biochar (HTGPB) in characterization and adsorption capacities for Enrofloxacin (ENR). Results showed that CSGPB exhibited more graphite-like structures with more active functional groups on the surface, and the equilibrium adsorption capacity of CSGPB (142.3 mg g-1) was 13.7 times of HTGPB (10.4 mg g-1) under identical conditions. Moreover, the adsorption behaviors including adsorption kinetics, isotherms and thermodynamics of CSGPB for ENR were fully investigated and discussed. Based on the above experiments, density functional theory (DFT) simulations were performed to reveal the interfacial interaction and adsorption mechanism. Results showed π-π interaction between quinolone moieties of ENR and graphite-like structures in CSGPB might be the dominant mechanism. As for the functional groups, the adsorption energies were -40.46, -15.21 and -5.96 kJ mol-1 for -SO3H, -OH and -COOH, respectively, which indicated -SO3H was the most active functional groups on the surface of CSGPB. This study provided a new sustainable perspective for the design of efficient biochars, and explored the interfacial interaction mechanism of antibiotics removal on biochars.

Facile extraction and characterization of cellulose nanocrystals from agricultural waste sugarcane straw.

BACKGROUND: Sugarcane straw is an available but largely ignored lignocellulosic biomass to obtain cellulose nanocrystals (CNCs) with highly crystalline, tunable surface chemistries and a wide-ranging adaptability. Herein, we utilized sugarcane straw to obtain pure cellulose via purification processes, followed by subsequent preparation of CNCs via sulfuric acid hydrolysis. The properties of the purified fibers and obtained CNCs were assessed by their composition, morphology, chemical structure, crystallinity and thermal stability. RESULTS: After the purification process, alkali-treated fibers (ATFs) contained 886.33 ± 1.25 g kg-1 cellulose, and its morphological analysis revealed a smooth and slender fibrous structure. The CNCs obtained by treatment with 64 wt% sulfuric acid at 45 °C for 60 min were isolated in a yield of 21.8%, with a diameter and length of 6 to 10 nm and 160 to 200 nm, respectively. Moreover, crystallinity index of these CNCs reached 62.66%, and thermal stability underwent a two-step degradation. Short-term ultrasonication after hydrolysis was employed to enhance isolation of the CNC particles and improve the anionic charge with higher value -38.00 mV. CONCLUSION: Overall, isolation and characterization results indicated the potential for CNCs preparation using sugarcane straw, in addition to offering a fundamental understanding of this material and indicating potential applications. © 2021 Society of Chemical Industry.

Reusable TsOH-H2SO4 Mixed Catalysis for Tandem Synthesis of Biodiesel and Oxygenated Fuel Additives, tert-Butyl Glycerol Ethers.

A mixture of p-toluenesulfonic acid and sulfuric acid (TsOH-H2SO4) was used as a catalyst with a good performance in transesterification of palm oil (PO) with methanol and etherification of crude glycerol with isobutylene (tandem synthesis). For TsOH-H2SO4 catalyzed biodiesel production, the reaction noticeably ran faster in comparison with TsOH or H2SO4 alone and also gave up to 99.9% of the conversion using MeOH/PO molar ratio 9:1 at 80℃, in the period of 4 h. After the whole transesterification process, the crude glycerol phase was separated and then reacted with isobutylene in the etherification process using isobutylene/glycerol molar ratio 9:1 at 80℃, in the period of 5 h reaction time, to give DTBG and TTBG (91.14%). In the case of the etherification in biodiesel, higher selectivity of DTBG and TTBG (99.39%) was obtained in comparison with an absence of biodiesel as the solvent. Furthermore, the catalyst could be reused for 6 cycles of tandem synthesis (transesterification and etherification). The TsOH-H2SO4 catalyst showed a good catalytic performance in tandem synthesis similar to TsOH and it could be recovered for reuse while TsOH could not be recovered. This process offers an attractive route for reuse homogeneous catalyst of tandem synthesis, the main by-product of biodiesel, to tert-butyl glycerol ethers - a value-added in applications as a valuable fuel additive.

Preparation, characterization, antioxidant and anti-inflammatory activities of acid-soluble pectin from okra (Abelmoschus esculentus L.).

Currently, there are few studies on acid-soluble pectin from okra, especially in biological activity for antioxidant and anti-inflammatory. In this study, the antioxidant properties of acid-soluble okra pectin components and their anti-inflammatory were explored. Firstly, two acid-soluble okra pectic fractions, namely crude acid-soluble okra pectin (CAOP) and acid-soluble okra pectin (AOP), were obtained and exhibited structural and compositional variation. The two pectic fractions contained a low degree of esterification (42.0-46.5%) and a relatively high uronic acid content (31.6-37.3%). AOP was composed of galacturonic acid (79.1 mol/%), galactose (4.3 mol/%), rhamnose (14.5 mol/%) and xylose (2.1 mol/%), and the molecular weight was 92.8 kDa. Morphological and thermal properties of acid-soluble okra pectin components were also investigated. Compared to CAOP, AOP expressed better antioxidant activity, and suppressed the NO production in LPS-induced RAW 264.7 macrophages. All the above results indicated that AOP had the potential to act as a natural antioxidant or a functional anti-inflammatory food, which would broaden the development and utilization of okra resources.

Efficient biobutanol production by acetone-butanol-ethanol fermentation from spent coffee grounds with microwave assisted dilute sulfuric acid pretreatment.

The integral valorization of potential sugars (cellulosic and hemicellulosic) from spent coffee grounds (SCG), a lignocellulosic residue, is proposed in this work. With this aim, the microwave assisted dilute sulfuric acid pretreatment has been optimized, leading to a hemicellulosic sugar recovery in the pretreatment liquid (HSRL) and an enzymatic hydrolysis yield of 79 and 98%, respectively, at 160.47 °C and 1.5% H2SO4. Moreover, the complete digestibility of cellulose (enzymatic hydrolysis yield = 100%) was also discovered for non-pretreated SCG, which is very interesting. Secondly, the production of biobutanol, an advanced biofuel, is also proposed from pretreated SCG enzymatic hydrolysate and pretreatment liquid achieved under optimal conditions. These were fermented by Clostridium beijerinckii, yielding 95 kg butanol/t SCG (dry matter) and 151 kg acetone-butanol-ethanol/t SCG (dry matter).

Superfine pulverisation pretreatment to enhance crystallinity of cellulose from Lycium barbarum L. leaves.

Superfine pulverisation (SFP) pretreatment of Lycium barbarum L. leaves was performed to obtain highly crystalline cellulose. Compared with other common pulverisation methods, SFP enhanced cellulosic crystallinity by 18.3 % and 8.4 %, with and without post-acid treatments, respectively. XRD and solid-state NMR analyses showed that SFP facilitated the exposure of amorphous substances (i.e., hemicellulose and lignin) to NaOH and H2O2. Large amounts of silicon (5.5 %) and aluminium (2.1 %) were found to incorporate into the crystalline regions of SFP-produced cellulose. Further FTIR and thermogravimetric analyses revealed that SFP-produced cellulose contained large amounts of hydroxyl groups, affecting the cellulosic crystallinity and thermal stability. These findings demonstrate the potential for SFP to serve as a green technology for production of highly crystalline and mineral-rich cellulose.

Clinical efficacy of targeted injection of drugs in combination with ozone in treatment of lumbar disc protrusion.

To investigate the clinical efficacy of targeted injection of drugs surrounding the protruded lumbar disc in combination with the ozone in treatment of lumbar disc protrusion. Between January 2017 and January 2019, a total of 120 patients with lumbar disc protrusion were recruited in this study and divided into the control group and observation group, with 60 patients in each group. Patients in the control group received the ozone treatment, while those in the observation group additionally took the targeted injection of betamethasone surrounding the protruded lumbar disc. Following one month of treatment, we compared the short-term efficacy, joint range of motion in bending forward or backward of the lumbar disc, limb function, life quality and functional disturbance before and after treatment. In the observation group, the short-term effectiveness rate was higher than that in the control group (P<0.05), while after treatment, the joint range of motion in bending forward or backward of lumbar disc in the observation group was improved when comparing to the control group (P<0.05). After treatment, BI and Fugl-Meyer scale were all higher in the observation than those in the control group (P<0.05), with a lower Oswestry score (P<0.05). Targeted injection of betamethasone surrounding the protruded lumbar disc in combination with the ozone performs well in short-term efficacy, conducive to the improvement of the lumbar disc function and limb function and alleviation in function disturbance. Thus, this strategy is worthy of being promoted in clinical practice.

Changes of nutrients and potentially toxic elements during hydrothermal carbonization of pig manure.

The effects of reaction temperature, residence time, sulfuric acid and potassium hydroxide on the total concentration and speciation of N and P, potentially toxic elements (salts and metal elements) of pig manure during its hydrothermal carbonization (HTC) were investigated. Concentrations of Cl, K, Na and Mg in the hydrochars were much lower but total N, P and nitrate-nitrogen (NO3--N) contents were significantly higher than in untreated pig manure. The acid-extractable fractions of Cu and Zn in hydrochars were 0.03-0.63 and 0.17-0.66 times lower than those in pig manure and decreased significantly with increasing reaction temperature. The addition of sulfuric acid (H2SO4) or potassium hydroxide (KOH) in HTC reduced the contents of P, Ca, Mg, Cl and heavy metal elements (HMEs) in hydrochars, and the removal rates of Cu and Zn were up to 55% and 59%, respectively. Overall, the rapid treatment of pig manure by HTC reduced the harm of salts and HMEs, and effectively recovered the nutrients in pig manure. The HTC under alkaline conditions was desirable for optimizing the main elemental composition of the hydrochars.

Bioremediation of gaseous methyl tert-butyl ether by combination of sulfuric acid modified bagasse activated carbon-bone biochar beads and Acinetobacter indicus screened from petroleum contaminated soil.

Combination of sulfuric acid modified bagasse activated carbon-bone biochar beads and Acinetobacter indicus screened from petroleum contaminated soil was the best condition for gaseous methyl tert-butyl ether (MTBE) removal. It was found that H2SO4 modified bagasse AC in powder form had higher adsorption capacity (989.33 mg g-1) than that in bead form (1.94 mg g-1). In addition, bone biochar in powder form (3.51 mg g-1) also had higher adsorption capacity than that in bead form (1.63 mg g-1). This was the fact that material beads contained high moisture content that inhibited the penetration of gaseous MTBE into the material. And a mixed material of H2SO4 modified bagasse AC-bone biochar beads had the highest adsorption capacity (2.22 mg g-1) compared to individual H2SO4 modified bagasse AC beads (1.94 mg g-1) and bone biochar beads (1.63 mg g-1) due to a mixed material had more rough surface and high surface area on its material. So, gaseous MTBE can penetrate through this material more easily. Although the maximum adsorption capacity of H2SO4 modified bagasse AC in powder form was the highest but microorganism cannot sustain and survive in this form for a long time. Therefore, the material beads were more suitable for microorganism to grow and degrade gaseous MTBE. Microorganism can degrade MTBE and caused no secondary wastes. Moreover, A. indicus was a novel strain for MTBE removal that has not been previously reported. Therefore, a combination of A. indicus-mixed material beads was a good choice for MTBE removal in a biofilter system.

Transition of cellulose supramolecular structure during concentrated acid treatment and its implication for cellulose nanocrystal yield.

Cellulose nanocrystals with cellulose I and II allomorphs (CNC-I and CNC-II) were prepared from eucalyptus cellulose I substrate by controlling the sulfuric acid hydrolysis conditions, including acid concentration (56-64 wt%), reaction temperature (45 or 60 °C) and time (10-120 min). The crystalline structures were verified by XRD and 13C-NMR. CNC-II only appeared at very restricted reaction conditions. The rapid cellulose supramolecular structure transition under sulfuric acid concentration of around 60 wt% resulted in an abrupt change in CNC yield. A maximal CNC yield of 66.7% was obtained at acid concentration of 58 wt% and reaction temperature of 60 °C. CNC-I exhibited spindle-shape, while CNC-II showed a twisted strip structure. The state of order in cellulose during the acid hydrolysis process has been studied using a coagulation method. A tentative model of CNC-I and CNC-II formation was then proposed. This work provided significant knowledge for the production of CNCs with high yield and controllable allomorph.

Efficacy of spent tea waste as chemically impregnated adsorbent involving ortho-phosphoric and sulphuric acid for abatement of aqueous phenol-isotherm, kinetics and artificial neural network modelling.

The current study emphasises on sorptive expulsion of phenol from aqueous solution using ortho-phosphoric acid (STAC-O) and sulphuric acid (STAC-H)-activated biochar derived from spent tea waste. STAC-O and STAC-H were instrumentally anatomised using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), BET surface area and thermal gravimetric analyser. Equilibrium and kinetic data were implemented for the investigative parametric batch study to prospect the influence of adsorbent dosage, contact time, initial concentration and pH for eradication of phenol from aqueous solution. The maximum phenolic removals by STAC-O and STAC-H are 93.59% and 91.024% respectively at the parametric conditions of adsorbent dosage 3 g/l time 2 h, initial phenol concentration 100 mg/l and pH 8. Non-linear regression of adsorption isotherms and kinetics was accomplished using the equilibrium data. Both the specimens were compared, and it delineated that Temkin isotherm model is contented. The maximum adsorption intakes for STAC-H and STAC-O were 185.002 mg/g and 154.39 mg/g respectively. Pseudo-second-order kinetic model was best fitted for portraying the chemisorption phenomena. Boyd kinetic and intra-particle diffusion model were investigated to elucidate the diffusion mechanism involved in the process. Desorption study was employed for determining the regeneration proficiency of the adsorbents using water, ethanol and NaOH with maximum 93% and 51.16% extrusion for STAC-O and STAC-H respectively. The process parameters involved in this study were further analysed using artificial neural network perusal to determine the input-output relationships and data pattern. The overall adsorption study along with cost estimation exhibited that bidirectional activation of spent tea biochar was prospective in abatement of phenol from aqueous media.

Effect-directed analysis by high-performance thin-layer chromatography for bioactive metabolites tracking in Primula veris flower and Primula boveana leaf extracts.

The genus Primula (Primulaceae) comprises species with high medicinal as well as ornamental values. Plants belonging to this genus are well recognized for their richness in bioactive constituents. The huge variety of secondary metabolites make their complete analysis impossible. In order to cope with this challenge, effect-directed analysis (EDA) via HPTLC coupled to structure elucidation techniques was applied on Primula species for the first time. As straightforward non-target bioanalytical technique, HPTLC-UV/Vis/FLD-EDA-ESI-HRMS hyphenates three different orthogonal dimensions, i.e. chromatography with spectrometric detection, biological/enzymatic assays and HRMS. The bioactive metabolites were determined in the middle polar extracts of two Primula species, P. veris (flower) and P. boveana (leaf). The bioactivity profiling comprised the antibacterial activity against Aliivibrio fischeri and Bacillus subtilis bacterial strains and acetyl-/butyrylcholinesterase (AChE/BChE) inhibition assays. The compounds were characterized and identified via their recorded spectral data (HRMS and 1H NMR). The results showed that linoleic and linolenic acids were the principle bioactive compounds present in the studied P. veris flower extract. In the P. boveana leaf extract, flavone, 2'-methoxy-, 2'-hydroxy- and 5,6,2',6'-tetramethoxyflavone (zapotin) were determined as active metabolites. The identification of zapotin, which was previously undescribed in the investigated plant, was considered as the strength of the straightforward non-target bioanalytical technique. Flavone turned out to be the highest potent metabolite, and at the same time, a multipotent compound referring to its various bioactivities discovered. An equivalency calculation of the HPTLC-AChE inhibition by flavone was performed with reference to the well-known inhibitor rivastigmine. As a result, the amount of flavone contained in 10.0 µg dry powder of P. boveana (corresponding to 0.1 µL extract) inhibited as strong as 4.5 µg rivastigmine. In other words, the flavone contained in P. boveana leaf extract powder turned out to be half as strong as the well-known AChE inhibitor rivastigmine.

A comparison between sulfuric acid and oxalic acid leaching with subsequent purification and precipitation for phosphorus recovery from sewage sludge incineration ash.

Wet chemical approach is widely applied for P extraction from incinerated sewage sludge ash (ISSA) due to the relatively simple process and low lost. In this study, H2SO4 and H2C2O4 were compared to recover P from ISSA through three steps of acid leaching, cation exchange resin (CER) purification and precipitation. Transformations of P speciation and mineral phases in ISSA from 600 to 900 °C were studied. The results showed that the ISSA samples were mainly composed of inorganic P (IP), and part of non-apatite IP (NAIP, mainly AlPO4) would transform to apatite P (AP, Ca3(PO4)2) with the increase in temperature. The ratio of NAIP to IP dropped from 71.9% at 600 °C to 53.7% at 900 °C. Effect of acid concentration on the leaching efficiency of P from the ISSA samples incinerated at different temperatures by H2SO4 and H2C2O4 was investigated, and the leaching behaviors of key elements of P, Ca, Al and Fe were compared. H2C2O4 exhibited a better performance than H2SO4 for the leaching efficiency of P. Severe sintering of ash particles occurred at temperature >800 °C inhibited the P leaching by H2SO4. During CER purification, the impurity elements in the H2SO4 leachate were easily removed by CER, whereas the Al and Fe elements in the H2C2O4 leachate were hardly removed due to the formation of anionic complexes between Al3+/Fe3+ and oxalic ions. Finally, high-purity struvite product was synthesized from the purified H2SO4 leachate, which could be directly utilized as a fertilizer with negligible environmental risk. Amorphous aluminum and iron hydroxyphosphates were obtained from the H2C2O4 leachate. This study provides insights for P recovery from ISSA samples by different acid leaching systems.

Experimental study on radon exhalation behavior of heap leaching uranium ore column with dilute sulfuric acid.

In order to study the radon release behavior when heap leaching uranium ores with dilute sulfuric acid, unleached uranium ores from a uranium mine in southern China were selected as test samples. Adopting parameters from leaching processes commonly used in uranium mines, a laboratory experiment was carried out for 21 days with a one-dimensional acid heap leaching experimental column. The surface radon exhalation rate of uranium ore column was determined by static accumulation method while spraying with deionized water and dilute sulfuric acid. The uranium leaching rate and ore column height for all 21 days of the experiment were also measured. The results show that (1) when sprayed with a leaching agent, the surface radon exhalation rate of uranium ore column initially increased with time sharply. After a maximum value was reached, the rate gradually decreased and stabilized. When the spraying stopped, the surface radon exhalation rate of uranium ore column initially decreased, before increasing until it tended to stabilize. (2) During the entirety of the 21-day leaching experiment, the cumulative leaching rate of uranium increased gradually with time. On the other hand, the surface radon exhalation rate of uranium ore column fluctuated, but the leaching of uranium from uranium ores had almost no effect on the radon exhalation rate. (3) There was no linear correlation between the surface radon exhalation rate and the residual height of ore column during leaching, but the collapsing event of ore column was the direct inducing factor of the fluctuation of surface radon exhalation rate.