A novel treatment processes of struvite with pretreated magnesite as a source of low-cost magnesium

Pyrolysis recycling of pig manure biochar adsorption material for decreasing ammonia nitrogen in biogas slurry

Biochar adsorption materials have a good removal effect on ammonia nitrogen in piggery biogas slurry. However, the cost of biochar adsorption material is still high. If these materials can be recycled several times, the cost can be significantly reduced. Therefore, this paper investigated a new process of biochar adsorption material (C@Mg-P) pyrolysis cycle for reducing ammonia nitrogen in piggery biogas slurry. The effects of pyrolysis process conditions (pyrolysis temperature and pyrolysis time) and number of recycling times on reducing ammonia nitrogen in biogas slurry by C@Mg-P were studied, a preliminary investigation on the reaction mechanism of C@Mg-P for reducing ammonia nitrogen in biogas slurry was conducted, and the economic feasibility of the pyrolysis recycling process was analyzed. It was found that the NH₃-N elimination efficiency by C@Mg-P was 79.16 % under the optimal conditions of 0.5 h and 100 °C. Second, C@Mg-P removed 70.31 % NH₃-N after recycling 10 times. Chemical precipitation, ion exchange, physical adsorption and electrostatic attraction were the potential reaction mechanisms for NH₃-N reduction by C@Mg-P. Moreover, C@Mg-P had a good decolorization effect on piggery biogas slurry with a 72.56 % decolorization rate. Compared with the non-pyrolyzed recycling process, the proposed process saved 80 % of the cost, thus representing an economically possible approach for pig manure biochar application in wastewater denitrification treatment.

Phosphorus recovery from incinerated sewage sludge ash using electrodialysis coupled with plant extractant enhancement technology

Phosphorus (P) is an integral mineral nutrient for the growth of plants and animals. As the increasing population worldwide, the demand for P resources keeps increasing. Therefore, it is necessary to recover P from secondary resources. Unlike conventional P recovery processes, this work focused on the recovery of P from incinerated sewage sludge ash (ISSA) using electrodialysis as the main technology coupled with plant extractants. In this study, Amaranthus and hydrolyzed polymaleic anhydride (HPMA) were used as P extractants, investigating the effects of HPMA concentration and pH of the compound agent on the migration of P and heavy metals from ISSA. The results showed that the concentration of HPMA and pH of the compound agent had a significant influence on the mobility of P and heavy metals. Meanwhile, the impacts of eggshell additions and voltage on the recovery efficiency of P was also studied by using waste eggshells as calcium sources. We found that when eggshells were added at 10 g/L and the voltage was 10 V, the recovery efficiency of P reached 96.05%. Moreover, XRD patterns revealed that the mineral phase of recovered P-containing products was predominantly hydroxyapatite, which had good environmental benefits. Generally, the favorable results have been achieved in the recovery efficiency of P and has practical implications for P recovery from ISSA.

Quantitative, morphological, and structural analysis of Ni incorporated with struvite during precipitation

Struvite precipitation is a promising strategy for the simultaneous recovery of nitrogen and phosphorus from waste streams. However, waste streams typically contain high amounts of metal contaminants, including Ni, which can be easily sequestered by struvite, but the behavior of Ni during struvite precipitation remains unclear. Thus, this study investigates the influence of Ni concentrations on struvite precipitation. The quantitative X-ray diffraction (QXRD) results revealed that the purity of struvite decreased from 96.6 to 41.1% with the Ni concentrations increased from 0.1-100 mg·L^-1. At lower Ni concentrations of 0.1-1 mg·L^-1, scanning electron microscopy (SEM) showed a roughened surface of struvite crystal, and this was combined with X-ray absorption near edge structure (XANES) data that indicated a stack of Ni-OH and Ni-PO₄ on struvite surface. At Ni concentrations of 10-25 mg·L^-1, Ni primarily crystalized as Ni-struvite (NiNH₄PO₄·6H₂O), as detected by QXRD. At higher Ni concentrations of 25-100 mg·L^-1, the co-precipitation of amorphous Ni phosphate(s) (e.g., Ni₃(PO₄)₂) and Ni hydroxide (e.g., Ni(OH)₂) was identified by XANES. Specifically, the X-ray photoelectron spectroscopy (XPS) analysis detected the formation of amorphous Mg hydroxide(s) and phosphate(s) at Ni of 25-100 mg·L^-1. The overall results revealed that Ni formed Ni-OH and Ni-PO₄ on struvite surface at 0.1-1 mg·L^-1, whereas Ni precipitated as separated phases (e.g. Ni-struvite, Ni hydroxide and phosphate) at 10-100 mg·L^-1. The existence of Ni disturbed the crystal growth of struvite and promoted the formation of Ni-struvite, amorphous products during struvite formation.

Crystal seed-enhanced ammonia nitrogen and phosphate recovery from landfill leachate using struvite precipitation technique

Nitrogen and phosphorous are limiting and crucial elements for all living organisms. The recovery of nitrogen and phosphorous as struvite gained attention due to its ecofriendly fertilizer application. In the present study, feasible recovery of NH₄⁺ -N available in the landfill leachate with addition of economically viable waste resources like sewage sludge and Mg²⁺ source as struvite is investigated. However, the fertilizer application of struvite depends upon its purity, which in turn is influenced by pH, molar ratio, and presence of other ions. Laboratory scale studies are conducted to find optimum pH and molar ratio. The results of the studies demonstrated the optimum pH being 9.5 along with PO₄^3- -P: Mg²⁺: NH₄⁺ -N molar ratio of 1:1.3:1 is the best condition for struvite formation. To further augment the struvite precipitation kaolinite seed is added to the solution and optimized seed dose is 20 g/L. Existence of Ca²⁺ and Na⁺ ions in the solution exhibits a negative impact on struvite precipitation. Response surface methodology is employed to understand the interactive influence of parameters on recovery efficiency. The recovered precipitate consists of 82.5% struvite with PO₄^3- -P: Mg²⁺: NH₄⁺ -N ratio 1:1.1:0.9. Also, bioavailability of PO₄^3- -P in the recovered precipitate is 89.3%; this signifies high performance of precipitate as fertilizer. Economic assessment highlights that the struvite production is profitable and the profit gained is 159.5$/m³.

The Flotation Separation of Magnesite and Limonite Using an Amine Collector

In order to reduce the iron impurities in magnesite ore and improve the purity of magnesium products, the difference in floatability between magnesite and limonite has been studied by using mixtures with a collecting agent—KD (cationic amine collectors, containing soluble components). Sodium hexametaphosphate, pH, sodium silicate, and sodium carboxymethyl cellulose were used as regulators. Adsorption mechanisms of the reagents on minerals were analyzed by a zeta potential analyzer and infrared spectroscopy. Sodium silicate increased the floatability of both minerals at 11.6. All the three regulators reduced the zeta potential of both minerals, while KD increased the zeta potential of magnesite and decreased the zeta potential of limonite. All the three regulators were likely chemically adsorbed on the surface of both minerals; KD has electrostatic adsorption on the surface of the minerals.

Thermal decomposition of struvite pellet by microwave radiation and recycling of its product to remove ammonium and phosphate from urine

The precipitation of struvite (MgNH₄PO₄·6H₂O) consumes many chemicals to completely remove ammonium and phosphate from urine and has the difficulty in solid separation from solution. This study proposed an alternative approach for the complete nutrient removal through recycling use of microwave-induced decomposition product of struvite pellet with sizes of 2-4 mm. Results showed that microwave radiation effectively decomposed the struvite pellet in an alkaline solution within 8 min. An increase in microwave power and NaOH concentration enhanced the decomposition. The double-layer structure of the pellet led to multiple paths of struvite decomposition. Active components of the decomposition product were newberyite, brucite, and amorphous MgNaPO₄ and MgHPO₄. The removal efficiencies of ammonium and phosphate from urine both reached 93% using the decomposition product at optimized P/N ratio and pH. Maximum recycles of 4 were recommended because further decomposition of the regenerated struvite pellets induced high losses of magnesium and phosphate. Calculations showed that the total cost of chemical consumption of the proposed approach was reduced by 47% compared with that of a conventional chemical struvite precipitation. Moreover, the volume index of the regenerated struvite pellets was 15 mL/g_P which was much lower than that of conventional struvite fines (116 mL/g_P), thereby indicating a better solid-liquid separation ability. Therefore, recycling of struvite pellets combining with microwave decomposition was chemical saving and easily separating of solid from liquid for the complete removal of nutrients from urine.

Application of MgO-modified palygorskite for nutrient recovery from swine wastewater: effect of pH, ions, and organic acids

In this study, MgO-modified palygorskite (MgO-PAL) was used for simultaneous recovery of ammonia nitrogen (AN) and phosphate, and the effects of pH, ions, and organic acids on nutrient recovery were investigated. The highest removal amount of AN and phosphate separately reached 42.6 mg/g and 69.8 mg/g at pH of 9.0, 0.6 g/L dosage of modified palygorskite, and 180 min of the reaction time. MgO-PAL provided a wide range of pH (3-9) for nutrient removal. Mg released concentration was tested to investigate the removal mechanisms. The individual presence of four cations (K⁺, Ca²⁺, Na⁺, and Mg²⁺) showed negative effect on AN removal at different mass concentrations. However, those cations, except Na⁺, exhibited positive influence on phosphate removal. Compared with SO₄^2-, CO₃^2-showed more negative effect on nutrient removal due to the reaction between Mg²⁺ and CO₃^2-. The results showed that the nutrient removal amount and the morphology and composition of collected products were not affected in the presence of acetic acid. Citric acid, humic acid, and fulvic acid displayed the inhibition effects on the morphology of the crystallized products.

Electrochemical acidolysis of magnesite to induce struvite crystallization for recovering phosphorus from aqueous solution

A novel struvite crystallization method induced by electrochemical acidolysis of cheap magnesite was investigated to recover phosphorus from aqueous solution. Magnesite was confirmed to continuously dissolve in the anolyte whose pH stabilized at about 2. Driven by the electrical field force, over 90% of the released Mg²⁺ migrated to the cathode chamber via passing through the cation exchange membrane. The pH of the phosphate-containing aqueous solution in the cathode chamber was elevated to the appropriate pH fit for struvite crystallization. The products were identified as struvite crystals by scanning electron microscopy and X-ray diffraction. Increasing the magnesite dosage from 0.83 to 3.33 g L^-1 promoted the phosphorus recovery efficiency from 2.2% to 78.3% at 3 d, which was attributed to sufficient Mg²⁺ supply. Increasing the applied voltage from 3 to 6 V improved the recovery efficiency from 43.6% to 76.4% at 1 d, since the enhanced current density of the electrochemical system markedly accelerated both the magnesite acidolysis and the catholyte pH elevation. The initial catholyte pH between 3 and 5 was found to benefit the phosphorus recovery due to the final catholyte pH fit for the struvite crystallization.

Facile thermal activation of non-reactive cryptocrystalline magnesite and its application on the treatment of acid mine drainage

In this study, the authors report a facile thermal activation of non-reactive cryptocrystalline magnesite and explore its application on the treatment of acid mine drainage (AMD). The primary aim was to optimize the calcination-water interface reactive conditions. Parameters evaluated include calcination temperature, calcination time, AMD-calcination temperature interface, and AMD-calcination duration interface. PHREEQC geochemical modelling was also applied to substantiate obtained results. The results indicated that the formation of MgO and CaO increase with an increase in calcination temperature and time. The optimum temperature and calcination time were observed to be 800 °C and 30 min in the furnace. The pH was observed to increase with an increase in calcination temperature and time but reached equilibrium at 800 °C and 30 min respectively. Geochemical modelling validated the formation of gypsum with attenuation in Ca ions and predicted the formation of MgSO_4(aq). Metal species were observed to precipitate with an increase in pH. At 700 °C, Fe was completely removed, while Al, and Mn were completely removed from an aqueous system at 800 °C. This novel study invented the new calcination condition for non-reactive cryptocrystalline magnesite and proved its potential application in wastewater treatment. The calcination conditions were very short and therefore will save industries energy due to replacement of uneconomical and less environmental friendly pre-treatment options that lead to environmental degradation.