Fluidized-bed Homogeneous Crystallization Research Articles

Homogeneous Crystallization of Nickel as Ni₃S₄ in a Fluidized Bed Reactor with Supersaturation Control

This study investigates the recovery of nickel sulfide (NiS) using fluidized bed homogeneous crystallization (FBHC), emphasizing the process from nucleation to crystallization. Sludge production in conventional chemical precipitation becomes a drawback in treating wastewater economically and efficiently. FBHC offers a promising alternative by minimizing sludge generation. The study examines various operational parameters, including hydraulic retention times (HRT), reflux ratio (R), initial nickel concentration, and static bed height (SBH), to optimize NiS recovery. Results show that FBHC achieves high total removal efficiency (TR) and crystallization ratio (CR), under the optimum condition of HRT = 15min, R = 8.3, initial nickel concentration = 147mg/L, and SBH = 35cm. The agglomeration of Ni(OH)2 was found to be crucial for the crystal growth during the surface oxidation of Ni3S4. This technological approach to wastewater treatment offers highly efficient heavy metal removal from wastewater.

Recovery of fluoride from wastewater in the form of cryolite granules by fluidized-bed homogeneous crystallization process

Aquatic ecosystems are harmed by high fluoride levels, which can disturb the equilibrium of water, plants, and animals and reduce biodiversity. Fluoride contamination in water sources can pose health risks and it is crucial to remove fluoride to prevent adverse effects on the environment and public health. Green technology is employed to recover fluoride from simulated fluoride-rich wastewater. The fluidized bed homogeneous crystallization (FBHC) process is an advanced methodology that removes contaminants from wastewater through supersaturation to recover nontoxic granules that can be used for other purposes. This study compared the fluoride recovery between batch crystallization and the FBHC process in terms of the molar ratio (MR) of [F−]:[Al3+] between [1] and [3] and the pH influence on the recovery and crystallization. The concentration of [Al3+] was varied at 37, 74, and 111 mM, along with the influent flow rates of 4, 8, and 12 mL·min−1. FBHC systems offer improved control of pH levels, creating a stable environment for crystallization. Unlike batch systems, these continuous operating systems are more resilient to pH fluctuations due to efficient mixing, maintaining a consistent pH throughout the process. Using Box-Behnken Design (BBD) for the FBHC, optimal conditions were 74 mM initial [Al] concentration, MR of [F−]:[Al3+] of [2]:[1], and 8 mL·min−1 influent flow rate resulted in 93 % fluoride removal (FR) and 91 % crystallization ratio (CR). XRD and SEM-EDS data showed similarities between the peaks and compositions of cryolite (Na3AlF6). FBHC was able to produce granules based on the reaction mechanism in the synthesis of cryolite.

Brine treatment using fluidized bed homogeneous crystallization technology for the simultaneous recovery of calcium and magnesium as dolomite-like granules

Fluidized bed homogeneous crystallization (FBHC) technology is an effective method to treat metal-contained wastewater at ambient temperature and pressure. Seawater desalination is common to produce fresh water and concentrated brine. This highly hardness-contained brine decreases the lifetime of membranes by fouling during desalination process. This study recovers calcium and magnesium by carbonate reagent from synthetic brine wastewater to be dolomite-like particles. The greatest total removal is 90.7 % for calcium and 76.0 % for magnesium, with a crystallization ratio of 89.5 % for Ca and 75.7 % for Mg, using a 40 min of hydraulic retention time, 9.5 of effluent pH, 2.0 of molar ratio, and 24 of reflux ratio. The effluent from the fluidized bed reactor (FBR) is aged in a sedimentation tank for 24 h to increase removal efficiency to 99.98 % for Ca and 84.7 % for Mg. XRD, SEM, FTIR, and Raman analysis reveal that particles are composed of CaCO3·H2O and MgCO3·3H2O with a dolomite-like structure and a core-shell morphology. In a real brine wastewater treatment by FBHC system, 86 % of Ca and 74 % of Mg are crystallized, so disposal costs are 75 % less than those for chemical precipitation, a conventional treating method. Therefore, FBHC technology has high potential to treat hardness-contained brine by reclaiming as dolomite-like granules.

Application of fluidized-bed homogeneous crystallization technology to carbon sequestration and recovery from flue gas

The Earth’s energy balance produced by human activity is the main factor in the complex relationship between greenhouse gases and global warming. The Taiwan Environmental Protection Agency reports that carbon dioxide makes up more than 95% of Taiwan’s most recent greenhouse gas emissions. This study used fluidized-bed homogeneous crystallization (FBHC) technology to recover carbonate in a simulated CO2-enriched flue gas. It was specifically designed to determine how carbonate removal and crystallization efficiency were affected by carbonate surface loading, the influence of the source of calcium ions, and interfering substances. Results revealed that the best surface loading at 55 kg m− 2 h− 1 achieved 93% removal and 84% crystallization efficiency. At 50 mg L− 1 of sulfate ions, the presence of more interfering compounds tends to reduce carbonate removal to 97% and 91% crystallization. Regarding X-ray diffraction data, the recovered carbonate crystals resembled calcium carbonate crystals. It has been demonstrated that carbonate can be recovered using FBHC technology as a method of CO2 capture and storage.

Recovery of nitrogen as struvite from swine wastewater: Comparison study of batch and continuous fluidized-bed crystallization process

The recovery of valuable compounds from waste supports the idea of a circular economy. Two systems were introduced in this study to recover nitrogen as struvite from swine wastewater, including batch stirred and fluidized-bed homogeneous crystallization (FBHC) systems. MgCl2 and NaH2PO4 were applied as precipitants to form struvite. In the batch stirred system, the removal efficiency of NH4+, Mg2+, and PO43− reached the optimum condition of 92.1 %, 75.6 %, and 91.1 %, respectively, under the operating conditions of pH 9 and an Mg/P molar ratio of 1.2. In the same operating conditions, the Crystallization ratio (CR) and Total Removal (TR) of the FBHC system reached 83.2 % and 89.1 %; 86.7 % and 90.6 %; 71.2 % and 76.1 % for NH4+, Mg2+, and PO43−, respectively. The XRD and FT-IR analyses confirmed the high purity and quality of the struvite solid product. However, the water content of the FBHC product is much lower than that of the batch-stirred system (5.8 % and 95.3 %, respectively). The great potential of swine wastewater as a nitrogen source for fertilizer production is evidenced by the high purity struvite product (>85.0 %).

Optimum operation condition of fluidized-bed homogeneous crystallization technology for the recovery of carbon dioxide captured in flue gas

The decarbonization of industry, particularly in "hard-to-decarbonize" sectors like combustion plants, poses a significant challenge due to the limited availability of low-carbon options. Carbon capture, utilization, and storage (CCUS) offers a promising solution to this challenge. Chemical precipitation is one method of converting CO2 into precipitated mineral carbonates, which can be stored and converted into valuable materials. This study explores fluidized-bed homogeneous crystallization (FBHC) technology for recovering carbonate from simulated CO2-enriched flue gas, resulting in stable calcium carbonate granules. Factors such as pH, carbonate concentration, reactor type, and reactants significantly impact carbonate removal and crystallization efficiency. Optimal conditions were found at 0.086 M input carbonate concentration, pH 9.0, and using a two-stage reactor, achieving 99.9 % removal and 93.2 % crystallization efficiency. Potassium-based absorbents yield higher crystalline intensity and larger granules compared to sodium. X-ray diffractometry confirms the composition of calcium carbonates, demonstrating FBHC's effectiveness for CO2 capture and storage. Utilizing calcium carbonate granules for carbon dioxide sequestration can potentially reduce emissions, pending resolution of investment and feasibility challenges.

Application of fluidized bed homogeneous crystallization for simultaneous recovery of Fe(II) and Cu(II) as particles from wastewater

The mixture of copper and iron often results in materials with favorable properties. The material production processes involving these metals including electroplating produce hazardous wastewater. In this study, the Fluidized Bed Homogeneous Crystallization (FBHC) process was applied to treat iron and copper-containing wastewater. The initial iron copper particles were successfully recovered from synthetic wastewater with [Fe]0:[Cu]0 of 2:1, the total metal concentration of 3 mM, at effluent pH = 7.75 ± 0.75, with the upflow velocity (U) of 1.76 m/h. The agglomerates hardening process is a crucial step for initial particle synthesis. The SEM analysis reveals the spherical particle's densified crust and porous core. The particle formation mechanism which includes the formation of the nucleus, attachment of precipitate flakes, and densification of particles was proposed after microscopic observation. The initial particles synthesized were used to initiate the treatment of synthetic wastewater at the operating condition pH = 7.75 ± 0.5, [Fe]0:[Cu]0 of 2:1, the total metal concentration of 3 mM, [CO32−]0:[M]0 = 1.2:1, and U of 28.66 m/h which results in the total metal removal of 99% and crystallization ratio of 90% and 88% for iron and copper respectively. The conditions were then applied to treat electroplating wastewater and resulted in the total metal removal of 99% for both iron and copper and a crystallization ratio of 83% and 79% for iron and copper, respectively. The treatment provided advantages in terms of treating larger amounts of sludge while eliminating the need to provide seed thus yielding a higher purity of product.

Copper recovery from treatment of simulated copper-iron wastewater using fluidized-bed homogeneous crystallization technology

Electroless plating wastewater contains highly soluble Cu-EDTA complex which poses challenges for copper recovery using conventional methods. These complexes are destroyed first using Fenton process producing treated solutions with iron concentrations that may interfere copper recovery. The purpose of this study was to confirm the influence of trace amount of iron on copper removal, crystallization, and copper salt recovery using fluidized-bed homogeneous crystallization (FBHC) process. By varying several parameters like pH, initial copper and iron concentrations, and metal and precipitant inlet flowrate and molar ratio, the optimized conditions include pHe of 6.5–7.0, inlet flowrate of 15 mL min−1, and MR of 1.5. The effects of variable copper (3.15–9.44 mM) and iron concentrations (0.36–1.08 mM) were examined. The addition of iron had no significant impact on copper removal mainly due to its minimal presence in the solution, but a trend of decreasing, then increasing, copper crystallization ratio was observed at higher iron concentrations. The study recorded copper removal and crystallization rates from 88% to 96% and 75% to 95%, respectively, with varying iron concentrations. Characterization analyses of precipitates confirmed predominant presence of malachite and azurite. The FBHC's ability to obtain high purity spheroidal solid salts enables resource recovery and catalyzes strategies for circular economy practices.

Selective granulation of trivalent iron into ferric hydroxide from bi-metal containing wastewater using Fluidized-Bed Homogeneous Crystallization technology

The traditional method that is used to treat the bi-metal-contained wastewater involves simultaneous chemical precipitation for the removal of both metals. However, recent trends in wastewater treatment emphasize the importance of recovery, recycling, and reuse. This study uses Fluidized-Bed Homogeneous Crystallization (FBHC) technology to selectively recover Fe(III) as granulated Fe(OH)3 from electroplating wastewater that contains iron and copper. For the treatment of a pure iron solution ([Fe(III)]0 = 650 mg/L), the optimal conditions include a pH value of 3.8, a reflux ratio (R) of 17.5, an up-flow velocity (U) of 35.9 m/h and a hydraulic retention time (HRT) of 17.9 min to give the maximum total removal efficiency (TR) for iron of more than 99.5%, and a crystallization ratio (CR) for iron of 93.6%. To treat real electroplating wastewater that contains iron and copper ([Fe(III)]0 = 1000 mg/L and [Cu(II)]0 = 500 mg/L), Fe(III) is effectively recovered as granules with a TR of 99% and a CR of 90%, and more than 90% of copper ions remain in the solution. SEM analysis observes that the product is an unseeded core-shell spherical particle. Additionally, XRD, FT-IR, and TGA results confirm that the product is an amorphous ferric hydroxide (Fe(OH)3) compound. A FBHC system has a high potential to separate iron and copper in a solution via a selective granulation process.

Sulfide recovery using fluidized bed homogeneous crystallization technology to produce nickel sulfide from wastewater that contains sulfides

Sulfide-containing wastewater, characterized by its foul odor, corrosiveness, and toxicity, can endanger human health. Fluidized-bed homogeneous crystallization (FBHC) avoids the excessive sludge production commonly associated with conventional chemical precipitation methods. In this study, FBHC is used to treat sulfur-containing synthetic wastewater. Furthermore, nickel-containing wastewater was utilized as a precipitant in the system, hence the advantage of simultaneous sulfur and nickel removal from the wastewater. The operating parameters, including pH, a precipitant dosage of [Ni2+]0/[S2−]0, and cross-sectional surface loading (LS, kg/m2h) are optimized. The optimum operating conditions of pH 9.8 ± 0.3, [Ni2+]0/[S2−]0 = 0.8, and LS = 1.5 kg/m2h results in total sulfur removal (TR) of 95.7% and crystallization ratio (CR) of 94.8%. The effect of organic compounds (acetic acid, oxalic acid, EDTA, and citric acid) and inorganic ions (NO3−, CO32−, PO43−, F−, and Cl−) on the nickel sulfide granulation process was discussed.

Recovering struvite from livestock wastewater by fluidized-bed homogeneous crystallization as a pre-treatment process to sludge co-digestion

Livestock wastewater can contain high levels of phosphates and trace amounts of various ionic species harming the environment and human health. These ions can be successfully removed from livestock effluent and recovered in a non-toxic crystal form via crystallization. The fluidized bed homogeneous crystallization (FBHC) technology is a cutting-edge pretreatment method that removes phosphate and ammonium by crystallizing struvite. The findings demonstrated a 37% removal for ammonium solutions alone, 38% with copper, 35% with zinc, and 33% when copper and zinc were present, while the crystallization efficiency was achieved at 35%, 33% with copper, 28% with zinc, and 26% with copper and zinc. For phosphate-containing solutions, 95% was removed, 81% with copper, 96% with zinc, and 88% with copper and zinc. Similarly, crystallization efficiency was attained at 87%, 60% with copper, 94% with zinc, and 81% when copper and zinc were combined with phosphates. For ammonium solutions, copper and zinc reduced the removal and crystallization efficiency at constant pH and increased at increasing pH. For phosphate solutions, the removal and crystallization efficiencies increased at increasing pH. However, zinc ions resulted in the highest removal, and crystallization efficiency for phosphate solutions was attained. Based on SEM, EDS, XRD, and XPS analyses, the peaks revealed the presence of struvite in the form of magnesium ammonium phosphate.

Fluidized-bed homogeneous crystallization of α-Al(OH)3 for continuous aluminum removal from aqueous solution: Parameter optimization and crystallization mechanism

Fluidized-bed homogeneous crystallization (FBHC) is utilized to recover dissolved aluminum from the solution. Aluminum is crystallized homogeneously using NaOH as a precipitant. Under the optimum pH of 9.7; cross-sectional surface loading (L) of 0.5 kg/m2.h; up-flow velocity (U) of 62 m/h, the total aluminum removal (TR%) in the FBHC reactor reached about 98.5% that is corresponding to the residual aluminum concentration of 10 mg/L. The crystallization ratio of aluminum pellets reached about 93%. The aging process of FBHC effluent solution in the sedimentation tank (SED) lowered the residual dissolved aluminum concentration to below 0.2 mg/L due to the polymorph change from amorphous Al(OH)3 to crystalline Al(OH)3. SEM image shows the round-shape pellet product of FBHC that consists of two different structures of the inner and outer parts due to the different operating supersaturation index. Meanwhile, XRD and FTIR patterns show that during 24 h of aging time, the precipitated compound was changed from amorphous Al(OH)3 to pseudo-AlOOH, and then α-Al(OH)3 crystal. Bayerite (α-Al(OH)3) was predominating the compound of the final pellet product. The production of low-moisture bayerite leads to a disposal cost reduction of up to 80%. FBHC proposed an alternative method to treat aluminum ions in the solution by reclaiming it as high separability and low moisture Al(OH)3 granulated crystal.

Application of low-solubility dolomite as seed material for phosphorus recovery from synthetic wastewater using fluidized-bed crystallization (FBC) technology

Fluidized-bed reactor technology was applied to recover phosphorus from solution via crystallization in a seeded (FBC, Fluidized-bed Crystallization) and unseeded (FBHC, Fluidized-bed Homogeneous Crystallization) system. Dolomite (CaMg(CO3)2) is applied as seed material to provide an existing surface in the seeded crystallization system. Under the optimum pH of 7.7, the presence of seed material in the FBC system enhanced the crystallization ratio of both phosphorus and calcium from 60% to 80%. The operating parameters, including - effluent pHe, up-flow velocity (U, m h−1), and cross-sectional loading (L, kg m−2 hr−1) were optimized in the FBC system. Under optimum conditions at pH 7.7, molar ratio of [Ca]0/[P]0=3.5/1, up-flow rate of 30 m h−1, and cross-sectional loading of 0.9 kg m−2 hr−1, the crystallization ratio (CR) and total removal (TR) of both phosphorus and calcium reached 85% and 92%, respectively. Based on the XRD and Raman pattern, it was confirmed the solid products consist of tricalcium phosphate (Ca3(PO4)2·xH2O) from both FBC and FBHC processes. An economic analysis shows that the disposal cost could be reduced from 0.92 US$ wastewater to 0.2 US$/m3. Phosphorus, encapsulated in a sparingly soluble crystalline form such as dolomite in the FBC system can be potentially used as a slow-release fertilizer and raw material for bio-ceramic and bioactive glass.

Recovery of phosphate as hydroxyapatite by fluidized bed homogeneous crystallization technique.

Phosphorous recovery from aqueous solutions gained substantial attention and this not only secure the food demand but also curtail the pollution of freshwater courses. In the current study, authors employed novel fluidized bed homogeneous crystallization (FBHC) technique to granulate the phosphorous as hydroxyapatite (HAP). FBHC technique nurtures the formation of high pure HAP crystals without seed addition and potential technique to recover phosphorous compared to other techniques. The key operational parameters influencing the HAP crystallization were analyzed prior to FBHC by batch analysis. From the batch study results, the range of pH and calcium to phosphorous molar ratio fixed for FBHC studies. Maximum phosphate removal and granulation efficiencies obtained were 91.25% and 82.55%, respectively, at 500mg/L phosphate concentration, pH 12, and calcium to phosphorous molar ratio 1.65. Box-Behnken design of response surface methodology was employed for evaluating interaction impact of process parameters on granulation efficiency. Granulation efficiency of 79.74% was attained at pH 11.83, calcium to phosphorous molar ratio 1.637, and reaction time 70.73h.

The recovery of sulfur as ZnS particles from sulfide-contained wastewater using fluidized bed homogeneous crystallization technology

Sulfide wastewater that is anthropogenically generated from industrial activities is highly corrosive, hazardous, and harms the natural ecosystem. This study uses a novel fluidized-bed homogeneous crystallization (FBHC) method to remove sulfide ions from an aqueous solution. Zinc is used as a precipitant to crystallize ZnS homogeneously in the FBHC reactor to reduce the sludge, which is commonly produced in a conventional chemical precipitation process. The optimal pH value, [Zn2+]0/[S2-]0 M ratio, sulfide cross-sectional surface loading (L, kg-S/m2.hr), and hydraulic retention time (HRT) for the system are established, to optimize the sulfur removal efficiency. The maximum crystallization ratio and the total removal efficiency for sulfur are 97.7% and 98.8%, respectively, at pH = 5.4, a [Zn2+]0/[S2-]0 M ratio of 1, a cross-sectional surface loading of 2.2 kg-S/m2.hr, and an HRT number of 6 with an initial sulfur concentration of 320 mg/L. The solid products are collected and identified as zinc sulfide (wurtzite) using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS).

Remediation of cobalt from semiconductor wastewater in the frame of fluidized-bed homogeneous granulation process

Green and sustainable strategies aim for the development of manufacturing processes that maximize the use of resources, instigating the semiconductor industry to adopt zero-liquid discharge policies. Complexity and variations in semiconductor wastewater effluents open an opportunity for resource recovery. One such opportunity is the potential recovery of heavy metals such as cobalt and/or copper in chemical-mechanical polishing wastewater, and inorganic anions such as phosphate from etching and acid cleaning. The present work demonstrates the capabilities of homogeneous crystallization in fluidized-bed reactor as treatment technology to process water effluents for industrial reuse while simultaneously recovering precious resources such as copper, cobalt and phosphate. Experimental results revealed that the optimum conditions were achieved at effluent pH of 7.75 – 8.0 and [PO4−3]/[Co2+] of 2.0. Uniform crystal growth was attained due to appropriate fluidization and proper collision of the particles at up flow velocity 40.11 m h−1 with 1.18 kg Co2+ m−2 h−1 loading. Performance was based on the removal/recovery capabilities of cobalt as heavy metal pollutant. The percentage of total cobalt recovered by granulation was 98.8%, whereas 99% cobalt removal was attained at optimal parameters. Coexistence of EDTA and citrate inhibits crystal growth, decreasing the metal granulation capability ~35%. Mixing of copper and cobalt ions in fluidized-bed homogeneous crystallization process was also investigated in which the highest granulation of 95.9% was attained at effluent pH of 6.50 for copper, and 96.8% at effluent pH of 7.50 for cobalt with an equimolar metal concentration of 7.0 mM and phosphate-metal molar ratio of 1.60. The granules recovered were analyzed using XRD and SEM-EDS. The recovered crystals were identified as mineral libethenite (Cu2(PO4)OH) and cobalt phosphate hydrate (Co3(PO4)2.8H2O).

Chemical precipitation at extreme fluoride concentration and potential recovery of CaF2 particles by fluidized-bed homogenous crystallization process

Excessive and industrial advances have increased fluoride quantity in the effluents. However, the environmental carrying capacity for fluoride is relatively slim immediately affecting both aquatic and terrestrial animals while its transport can further contaminate the water source. To protect the public and the environment, different environmental agencies globally set their respective effluent standard restricting F- concentration to 15 mg/L as the median value. However, various processes from previous investigations have mostly been limited in treating 100–1000 mg F-/L with secondary pollution commonly overlooked. Re-assessing the available defluoridation technologies, chemical precipitation has still been the most feasible among the technologies, especially extremely high fluoride concentrations. In this study, fluoride removal through chemical precipitation was investigated using conventional precipitation and fluidized-bed homogeneous crystallization. Parameters such as a wide range of initial concentrations from 100 to10,000 mg/L and pH 2.0–11.0 under conventional precipitation were varied and analyzed. To reduce high water content sludge, a 550-mL cylindrical glass was modified to simulate a fluidized-bed reactor to investigate homogenous crystallization varying influent concentration, bed-support size, and fluid flow. Results showed that chemical precipitation could effectively remove fluoride even at very high fluoride concentrations ranging from 1,000 to 10,000 mg/L. Alternatively in the fluidized-bed granulation process, an initial very low flow without recirculation flow was required to initiate particle formation. The predominant size of the recovered particle was < 0.2 mm which was relatively heavy atypically not reaching the upper region of the reactor. Under the observed optimum condition with an initial fluoride concentration of 450 mg/L, both total removal and crystallization ratio could reach ∼ 98% efficiency lowering fluoride concentration to < 15.0 mg F-/L within 7 days.

Nutrients recovery from urine through struvite formation using lab-scale fluidized-bed homogeneous crystallization reactor

Phosphorus (P) is considered the most important micro-element needed for every living thing. Even though they have limited amount, P and nitrogen (N) are responsible for eutrophication in water bodies. This paper aimed to give an insight into the removal efficiency of nutrients and struvite crystallization of slowly soluble fertilizer MgNH4PO4.6H2O, which is also called NH4+-struvite. Besides, using fluidized bed homogeneous crystallization (FBHC) system can reduce impurities in granular struvite generated during the reaction as the advantage function itself. The results showed the changes in pH, magnesium (Mg2+), phosphate (PO43--P), ammonium (NH4+-N), and appearance of spontaneous struvite precipitation over time. Using synthesis urine sample with adjusted pH and Mg2+ concentration to determine the optimal conditions for granular NH4+-struvite recovery to maintain Mg and P removal efficiency up to 99% in steady state. In this study, the removal efficiency of N was about 80 – 85% maximum. The initial results indicated the feasibility of simultaneous crystallizing NH4+-struvite which is mentioned above. It could easily form at pH around 8 – 9. On the other hand, urea hydrolysis makes a pH increase in urine from 6.5 to less than 9.0 at room temperature. This might cause a heavy impact on the NH4+-N crystallization during the formation of granular struvite if there has no suitable NH4+-N pretreatment options. For Mg recovery, the concentration of Mg is detrimental in the creation of struvite. This will bring better removal efficiency if there is an available Mg source in nature which can be reused directly in an environmentally eco-friendly way. The total mass of struvite precipitate obtained in the form of nuclei corresponds to 200 g/m3 of urine during 24 days operation.

Recovery of iron(II) and aluminum(III) from acid mine drainage by sequential selective precipitation and fluidized bed homogeneous crystallization (FBHC)

Acid mine drainage (AMD) released from gold and coal mining contains a large quantity of heavy metals, thus being a threat to the surrounding ecosystem. The recovery of metals from AMD can both address the potential contamination and bring more economic profits. In this study, the sequential selective precipitation and fluidized bed homogeneous crystallization (FBHC) were integrated to recover iron(II) and Al(III) from real AMD wastewater. The selective precipitation of Fe was optimized by adjusting pH. The FBHC recovery of Al performed its best at pH 9.25 ± 0.2, molar ratio of [H2O2]/[Al(III)] = 2.0 and up-flow velocity (U) = 30.5 m/h. Iron(II) and Al(III) were recovered in the form of iron hydroxide (Fe(OH)3) and bayerite (α-Al(OH)3) pellets. Removal efficiencies were as high as 99.7% and 99.3% for Fe(II) and Al(III), respectively. A brief cost-benefit estimation was performed and showed that the estimated profit gained from field-scale recovery of Fe(II) and Al(III) would be $1.31/m3-AMD.

Recovery of magnetite from fluidized-bed homogeneous crystallization of iron-containing solution as photocatalyst for Fenton-like degradation of RB5 azo dye under UVA irradiation

Iron recovery from wastewater as magnetite (Fe3O4) pellets was performed in a fluidized-bed homogeneous crystallization (FBHC) process. The catalytic effectiveness of magnetite in the heterogeneous degradation of RB5 azo dye was evaluated. The key parameters of FBHC, including effluent pH, cross-section loading (L, kg/m2.h), initial iron concentration ([Fe(II)], mg/L), and inlet supersaturation (S), were optimized to maximize the total iron removal (TR, %) and crystallization ratio (CR, %) from a fluidized-bed reactor. Under the conditions of pH = 8.5–9.5 and [Fe(II)]in = 100 – 500 mg/L, the TR and CR values reached 99% and 77%, respectively. The magnetization and coercivity of the recovered Fe3O4 pellets were analyzed to confirm the magnetic characteristic. A Fenton-like degradation of RB5 azo dye was activated using the Fe3O4 pellets under UVA irradiation, pH = 2.75 – 3.0, initial peroxide concentration of 10 mM, and catalyst loading of 2 g/L. The efficiencies of decolorization and mineralization reached about 98 – 99% and 60 – 68%, respectively. FBHC method benefited the recovery of high-purity metal oxides and the production of a low quantity of sludge. Magnetic pellets transformed from the dissolved iron in wastewater were promising materials to reuse as a photochemical reactant for organic pollutant degradation.