Hydroxide Precipitation Process Research Articles

Enhanced biogas yield in anaerobic digestion of citric acid wastewater by pre-treatment: The effect of calcium hydroxide precipitation and electrocoagulation process

During the production and use of citric acid (CA), which is frequently used in food, chemistry, metallurgy and other related industries, wastewater with high organic load and acidity is generated. Discharge of these wastewaters into the receiving environment without adequate purification causes serious pollution problems. However, treating such wastewater with hybrid processes allows both the formation of valuable by-products and an increase in the degree of purification. In this study, the biogas production potential of citric acid wastewater (CAWW), which was pre-treated by chemical precipitation and electrocoagulation (EC) processes, was investigated. Pre-treatment experiments were designed using Box-Behnken Design (BBD) and chemical oxygen demand (COD) concentrations after hydrated lime (Ca(OH)2) precipitation and EC processes were determined as 4960 mg/L and 5120 mg/L, respectively. The pre-treated CAWW were finally used for the secondary treatment by anaerobic digestion (AD) process. After AD process COD degradation determined as 67% and 98% for Ca(OH)2 precipitation and EC process, respectively. In addition, the biogas production of the pre-treated CAWW increased approximately 2 and 7 times for the Ca(OH)2 precipitation and EC processes, respectively, compared to the untreated. The methane (CH4) content of the produced biogas increased by 18% and 50% for Ca(OH)2 precipitation and EC processes, respectively. According to 48-hour acute toxic test result, daphnia mortality decreased from 50% concentration of CAWW after AD, even 10% concentration is non-toxic to daphnia. In conclusion, the complementarity of Ca(OH)2 precipitation and EC processes with AD promoted both the removal of organics from wastewater and the production of valuable by-products.

Recycling of waste carbon residue from spent lithium-ion batteries via constant-pressure acid leaching

Waste carbon residue (WCR) was efficiently detoxicated and regenerated to high-purity graphite (PGC) used in lithium-ion batteries through the constant-pressure acid leaching technique. The leaching conditions were optimized by the combination of orthogonal and single-factor experiments. Results show that PGC with 99.5% purity is regenerated at temperature of 60 °C, initial acid concentration of 12%, leaching time of 180 min, and liquid-to-solid ratio of 25:1, satisfying the requirements of commercial graphite. Meanwhile, the sodium hydroxide precipitation process was designed to recover valuable components from leachate efficiently. Ni, Co, Mn, and Al recoveries reach 96.92%, 87.5%, 97.83%, and 92.17%, respectively, at pH=11. Moreover, the co-product NaF can be recovered with purity over 99% via evaporative crystallization. The loss rate of fluorine is less than 0.5%, thereby eliminating the pollution risk of fluorine to the environment. The proposed process shows considerable environmental and economic benefits.

Enhanced oxalate-induced degradation of organic dyes using magnetic photo-Fenton catalysts based on CuFe2O4-Fe2O3 composites

ABSTRACT The aim of this study was to synthesise magnetic CuFe2O4-Fe2O3 composite materials with enhanced photo-Fenton catalytic activity for the degradation of organic dyes in the presence of oxalic acid as radical-producing source. The composite catalysts were prepared by a simple hydroxide precipitation process followed by an annealing at 300°C with different annealing times. Their phase composition, morphology, surface atomic composition, surface functional groups and magnetic properties were characterised by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and vibrating sample magnetometry. The catalytic tests were carried out using methylene blue as a cationic dye and methyl orange as an anionic dye. According to the results, all CuFe2O4-Fe2O3 composite catalysts exhibited significantly higher photo-Fenton activities than CuFe2O4 sample under UVA light and visible light, which can be attributed to the enhanced content of Fe species and the high roughness observed on composite surface. These composite catalysts were found effective in degrading both cationic and anionic dyes although the decomposition of methyl orange was more difficult than that of methylene blue. Moreover, oxalic acid was also experimentally proved to be an excellent radical-producing source, which is superior to H2O2, in our photo-Fenton catalytic system. When the annealing time used in the synthetic procedure was extended, the catalytic performance of composite samples tended to increase but their magnetic properties were reduced, revealing that the annealing time is an important factor to be considered for the preparation of magnetic photo-Fenton composite catalysts.

Influences of New Synthesized Active Seeds and Industrial Seed on the Aluminum Hydroxide Precipitation from Sodium Aluminate Solution

The aluminum hydroxide precipitation process from sodium aluminate solution was studied by adding the new synthesized active seeds and industrial seed separately. The results show that the precipitation rate reached 47, 81, and 68% at 60 h by adding industrial seed, seed A, and seed B (active seeds), respectively. Specific surface area, composition, morphology, and particle size distribution of seeds/precipitated products from supersaturated sodium aluminate solutions were investigated by Brunauer, Emmett, and Teller (BET) analysis, X-ray crystallography (XRD) analysis, Scanning electron microscope (SEM) images, and Power-spectral-density (PSD) analysis. Also, to study and understand the functional groups on the surface of seed/precipitated products and precipitation mechanisms, Fourier-transform infrared spectroscopy (FTIR) analysis was recorded. The result showed that the precipitation rate of the active seeds is higher than that of the industrial seed owing to the higher surface area, more active sites, crystal defects, and finer particle size that cause rise to nucleation for gibbsite. Also, improved precipitation of aluminum hydroxide from sodium aluminate solution may be due to the predominant phase crystallized of bayerite in the composition of active seeds. The FTIR analysis shows that the decline of the precipitation process in the presence of industrial seed may be due to oxalate–Al bonds and the impurity of carbonate.

Effect of reaction conditions on agglomeration of aluminum hydroxide in the recovery of waste aluminum-catalyst

Water-soluble waste salts, especially those contain harmful ions, are a great threat to soil, water, air, and human health. NaAlCl4 waste salt, containing harmful Al3+ ion, is massively by-produced in the manufacture of dichlorophenylphosphine (DCPP) and remains a big issue to both industry and environment. In this work, we intensively investigated the aluminum hydroxide precipitation process during the recovery of NaAlCl4 waste salt via acid-base reaction. The aluminum hydroxide crystallized under different conditions was monitored and characterized using XRD, TG, SEM, and Zeta potential. The effect of precipitation pH and temperature on crystal form, gel content, agglomerate size distribution, and moisture content of filter cake were studied. Precipitation pH was found to influence both gel-precipitation conversion and agglomerate state, but its effect varied under different temperature, indicating complex gelation and agglomeration processes. Temperature, however, has similar effect at different pH conditions that low gel content and hardened agglomerate can be achieved with increasing temperature due to intensified particle movement and collision. In addition, NaCl has little effect on the crystal form of aluminum hydroxide even though some initial NaCl exists in the solution. Then, the precipitation mechanism was proposed, in which agglomerate void filling process was discovered and verified via porosity analysis. Furthermore, the precipitation process was optimized and a drop of 25.16% in filter cake moisture content was achieved which can lead to a better separation of Al3+ and Na+ and a higher efficient recovery of the waste salts.

Microencapsulated phase change materials with high heat capacity and high cyclic durability for high-temperature thermal energy storage and transportation

Latent heat storage (LHS) technology employing phase change materials (PCMs) has received great attention as an alternative to conventional solid sensible heat storage (SHS) for future high-temperature energy utilisation systems. In this study, we report the synthesis of a core-shell type microencapsulated PCM (MEPCM) consisting of Al-25wt% Si microspheres (mean diameter of 36.3μm and melting temperature of 577°C) as the core (PCM) and Al2O3 as the shell. The MEPCM was prepared in two steps involving (1) the formation of an AlOOH precursor shell on the PCM microspheres by a hydroxide precipitation process in hot water and (2) heat-oxidation treatment in an O2 atmosphere to form a stable Al2O3 shell. In particular, the effects of heat-oxidation temperature on the shell morphology, shell crystal structure, mechanical strength, heat capacity, and cyclic durability of the prepared MEPCMs were examined. The resultant MEPCM is composed of a stable α-Al2O3 shell and Al-25wt% Si core with an effective void inside the core to allow for volume expansion of the PCMs during solid-liquid phase transitions. The heat capacity measured for this material is five times higher than that of conventional solid SHS materials. Additionally, the MEPCM exhibits excellent durability up to 300 heating and cooling cycles under oxygen atmosphere. Consequently, it can potentially be used in the next-generation LHS-based high-temperature thermal energy storage and transportation systems.

A comparative study on surface morphological investigations of ferric oxide for LPG and opto-electronic humidity sensors

In the present work nanostructured ferric oxides were synthesized via hydroxide precipitation method without using any surfactant and size selection medium. The surface morphologies and structure of samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The structural analysis confirmed the formation of Fe2O3 with α-phase and rhombohedral structure. Optical and thermal properties were investigated by using UV–visible absorption spectroscopy and differential scanning calorimetry (DSC) techniques. Pelletizations of materials were done using hydraulic press and these pellets were investigated with the exposition of liquefied petroleum gas. Variations in resistance of the pellet with time for different concentrations of LPG were recorded at room temperature (27°C). The maximum value of average sensitivity was found ∼5 for 5vol.% of LPG. Our results show that the LPG sensing behavior was inspired by the different kinds of surface morphologies of Fe2O3 and inferred that the spherical porous nanoparticles synthesized via hydroxide precipitation process (S-3) had best response to LPG.

Electron microscopy study of intragranular nanoporosity and the occurrence of local structural disorder in cubic BaTiO3 nanopowders from alkoxide–hydroxide precipitation process

The evolution of phase and defect structure in BaTiO3 nanopowders synthesized by an alkoxide–hydroxide process in benzyl alcohol under reflux conditions were investigated. As-prepared powders were heat-processed at temperatures ranging from 250 to 850°C. X-ray powder diffraction (XRD) showed that BaTiO3 remained cubic with crystallite size below 30nm after heat treatment up to 850°C. Internal pores of 1–2nm diameter inside the crystallites were well visible with transmission electron microscopy (TEM) at processing temperatures between 250 and 600°C. Their presence was confirmed by infrared spectroscopy (FT-IR) and is attributed to accumulation and curing of lattice hydroxyl defects. No tetragonal phase was detected by XRD up to 700°C. However, Raman spectroscopy (FT-RS) revealed Raman activity in all cubic materials. This was attributed to local tetragonal and orthorhombic distortions, resulting from the presence of internal nanopores. Considering that the nanopores constitute a relatively large fraction of the total volume of the nanocrystals, the internal strain may be substantial. Hence, a relatively high temperature is necessary not only to cure the hydroxyl defects, but also to release the internal strains accumulated in the crystals upon volume diffusion and sintering. Therefore, the cubic-to-tetragonal phase transition was observed only after heat treatment at 850°C, when the occurrence of a tetragonal phase was accompanied by substantial grain growth to ∼100nm size.

Heavy Metals in Wastewater: The Effect of Electrolyte Composition on the Precipitation of Cadmium(II) Using Lime and Magnesia

The effect of effluent composition on the efficiency of hydroxide precipitation of Cd(II), using both lime and magnesia as precipitants, has been modelled by the solubility domain approach in order to provide wastewater effluent treatment limits, and has been experimentally validated. Common anionic species such as Cl−, SO42− and CO32− have been treated. Solubility domain calculations were based on those phases that were found to determine metal solubility for systems representing the upper and lower limits of potential effluent chemical compositions. The isolated phases were found to resemble their mineralized counterparts, although in several cases exhibited a lower degree of structural order. Experimentally determined Cd(II) solubilities were generally encompassed within the calculated solubility domains, indicating that solubility domain predictions provide effluent treatment quality assurance ranges for the hydroxide precipitation process. The formation of gypsum (CaSO4.2H2O) and calcite (CaCO3) at higher SO42− and CO32− concentrations as secondary precipitates using lime as the precipitant, and the hydroxy-sulfate Mg2(OH)2SO4.xH2O, nesquehonite (MgCO3.4H2O), hydromagnesite [Mg5(OH)2(CO3)4.4H2O] and brucite [Mg(OH)2] when employing magnesia was shown to have little effect on the observed residual Cd(II) solubility, although Mg(OH)2 did promote β-Cd(OH)2 formation in the Mg2+-containing Cd(II)/Cl− and Cd(II)/SO42− systems.

Influences of novel surfactants on the physicochemical properties of sodium aluminate solution relevant to the aluminium hydroxide precipitation process

The physicochemical properties of sodium aluminate solutions are modified by adding different surfactants, and the variations of the surface tension, viscosity as well as the conductivity are investigated in detail. The modification of the properties of the solution is correlated with the aluminium hydroxide precipitation process from the solution (Bayer process). The results indicate that the precipitation ratio, the crystal size, as well as the intensity of the Al(OH)3 products can be enhanced after addition of certain types of surfactants. The chemical compositions of the surfactants are reported and it can be shown that novel types of surfactants prepared by mixing different, relatively cheaper components exhibit the potential to replace the more expensive recipés commercially available. These improvements to the precipitation process are interpreted as being due to modification of the properties of the sodium aluminate solution after addition of the surfactants.

共沈法を用いた廃蛍光体スラッジからの赤色蛍光体（Ｙ２Ｏ３ ： Ｅｕ｀３＋´）の合成

The coprecipitation behaviors of leaching solution and their sintering conditions have been examined to synthesize red phosphor (Y2O3:Eu3+) from phosphor sludge contained in waste fluorescent lamp. At first, the recovery of rare earth elements and the removal of impurity in the leaching solution were investigated by treatment processes such as hydroxide and oxalate precipitations. The drying process of coprecipitation reaction product was examined by freeze-dry and air-dry. The synthesis behavior of red phosphor (Y2O3:Eu3+) was also investigated by changing some factors such as temperature, time and flux. The experimental results obtained are summarized as follows:(1) The homogeneous Y and Eu oxalate precipitations were produced by adding oxalic acid into leaching solution under the dispersion using ultrasonic stirring and the desiccation using freeze-dry.(2) Y and Eu precipitations were sintered at 1,473 K for 144 ks under the addition of 1 % barium borate as a flux. Red phosphor (Y2O3:Eu3+) sintered had crystal size more than 0.2μm and average particle size of 5-6μm.(3) Impurity elements in leaching solution were efficiently removed by hydroxide precipitation process, in which leaching solution was retained at less than pH 5.0 and by oxalate synthesis process, in which oxalic acid was added to use 3 times the molar quantity of Y and Eu hydroxides. In these treatments, recovery of Y and Eu were about 85 %, respectively.(4) Synthesis process of red phosphor (Y2O3:Eu3+) from waste phosphor sludge contained in fluorescent lamp was established by using simulate leaching solution. On the basis of these treatment methods, rare earth powder of red phosphor was synthesized from waste phosphor sludge.Luminescence properties of rare earth powder synthesized were in fairly agreement with these of commercial red phosphor. Rare earth powder synthesized in this work may be used substantially as a red phosphor.

A case study of microwave processing of metal hydroxide sediment sludge from printed circuit board manufacturing wash water

The large quantity of wash water used in the electroplating and etching process in the manufacturing of printed circuit boards (PCBs) contains a high level of heavy metal ions (Cu ++, Zn ++, Ni ++, Cr +++, Pb ++). These potentially toxic ions are removed from the wash water effluent through a polyelectrolyte flocculation and hydroxide precipitation process during which a hydroxide sediment sludge rich in metal ions and polymers is generated. This sediment sludge possesses some unique characteristics and properties in terms of composition, fine particle size distribution, high specific surface area, and a tendency to agglomerate after drying. Direct disposal of this classified “special waste” (Department of Environment of Northern Ireland, The Special Waste Regulations, Northern Ireland, 1998) at landfill sites may cause serious soil and underground water pollution through a gradual ionic leaching process. This paper describes an experimental investigation, exploratory in nature, which employs microwave radiation for detoxification of the sediment sludge through microwave heating, drying and metal ion immobilization within the sediment solids. The effectiveness of microwave assisted binding and immobilization of the metal ions within the sediment solids was studied in conjunction with an evaluation of microwave energy efficiency in comparison to the more conventional convective heating and drying processes. Given a sufficient amount of microwave radiation, leaching of Cu 2+ and Pb 2+ was reduced by 2700% and 1080%, respectively, over a period of 12 weeks, and further leaching was not detectable within six months at simulated local landfill aqueous conditions. This paper also attempts, through experimental observation, to add to the very limited understanding of the complex interactions and binding of free metal ions with the polymeric materials and metal hydroxides under the influence of an electromagnetic field. The high specific surface of the sediment solids and their adsorption properties were further explored and characterized in a study of adsorption of reactive dyes by the microwave processed solids.

Effect of electrolyte composition on zinc hydroxide precipitation by lime

The effect of effluent composition on the efficiency of the hydroxide precipitation of Zn 2+ modelling lime (CaO) as a precipitant has been predicted using the solubility domain approach and experimentally validated. Solubility domains were based on the phases that were found to be solubility limiting for systems representing potential effluent chemical composition limits. All such phases were found to resemble their mineralized counterparts with a lower degree of structural order. The generated solubility domains generally encompassed the experimentally observed solubilities, thus providing effluent treatment quality assurance ranges for the hydroxide precipitation process. The presence of calcite (CaCO 3) and gypsum (CaSO 4.2H 2O) as secondary precipitates had little effect on the observed residual zinc solubilities. Validation of the solubility domain approach using real industrial wastewater was accomplished.

Heavy metals in wastewater: Modelling the hydroxide precipitation of copper(II) from wastewater using lime as the precipitant

The effect of effluent composition (Cl −, SO 4 2− or CO 3 2−) on the efficiency of the hydroxide precipitation of Cu(II) modelling lime (CaO) as the precipitant has been predicted using the solubility domain approach and has been experimentally validated. Solubility domains were based on the phases that were found to be solubility-limiting for systems representing potential effluent chemical composition limits. The generated solubility domains generally encompassed the experimentally observed solubilities, thereby providing effluent treatment quality assurance ranges for the hydroxide precipitation process. The presence of gypsum (CaSO 4.2H 2O) and calcite (CaCO 3) as secondary precipitates had little effect on the observed residual Cu(II) solubilities, with Cu(II) mobility being governed by the least-soluble kinetically precipitated (rather than thermodynamically favoured) phase in the system under study.

Microstructural characterization of MgFe 2O 4 powders

The electrical properties of MgFe 2O 4 spinel are such that it is suitable as a sensing element for humidity measurement devices. One of the most important targets to be reached for this kind of application is the possibility of designing the microstructure of spinel powder compacts, because of its strong relationship with the spinel humidity-sensitive electrical properties. Thermal decomposition of precipitated precursors allows one to achieve this target. This paper deals with the microstructural characterization of MgFe 2O 4 spinel powder samples, obtained by thermal decomposition of various hydroxide precursors, in comparison with that of MgFe 2O 4 samples prepared by solid state reaction of the corresponding oxides. The results demonstrate that the hydroxide precipitation process is effective in varying the morphology and the microstructure of the final MgFe 2O 4 powders with respect to that obtained by solid state reaction.