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The effects of rare earth elements (Ce and Y) additions with the same content (0.3 wt.%, mass fraction) on microstructure evolution and mechanical properties of the Al-11.0Zn-3.1Mg-1.22Cu-0.1Sr-0.2Zr-0.1Ti alloy (base alloy) were investigated. The addition of Ce and Y refined the grain size and led to aging precipitates, which were dominated by the fine and compactly distributed GP (Guinier Preston) zones and the formed η′ (MgZn2) phase, improving the tensile properties of the alloy. The Ce-containing alloy possessed the highest tensile strength and elongation of 768.5 MPa and 8.0%, respectively. Meanwhile, the large atomic radius and low electronegativity of Ce and Y led to the discontinuous distribution of grain boundary precipitates (GBPs) and the broadening of the precipitate-free zones (PFZs) in the alloys, resulting in the improvement of intergranular corrosion resistance (IGC) of the rare earth modified alloys compared with the base alloy, with the best results for the Y-containing alloys. [ABSTRACT FROM AUTHOR]

To achieve highly efficient extraction of phosphorus (P) and comprehensive utilization of phosphate tailings, a two-stage leaching-precipitation method was proposed. Phosphate tailings primarily consisted of dolomite, fluorapatite, and quartz. During the first-stage leaching, the large majority of dolomite was selectively dissolved and the leaching efficiency of Mg reached 93.1 % at pH 2.0 and 60 °C. The subsequent second-stage leaching of fluorapatite was performed and the P leaching efficiency was 98.8 % at pH 1.5 and 20 °C, while the quartz remained in the residue. Through two-stage leaching, a stepwise leaching of dolomite and fluorapatite was achieved. After chemical precipitation, calcium phosphate with a high purity of 97.9 % was obtained; and the total recovery efficiency of P exceeded 98 %. The obtained calcium phosphate can be a raw material in the phosphorus chemical industry, while the Mg-rich leachate and the final quartz-rich residue have the potential for Mg extraction and the production of mortars or geopolymers, respectively. The two-stage leaching-precipitation process could significantly reduce the leaching costs, and enhance the reaction rates. It is expected to realize a volume reduction and efficient resource utilization of the phosphate tailings by using this sustainable and promising solution. • A new method of P extraction and utilization of phosphate tailings was proposed. • A stepwise dissolution of dolomite and fluorapatite was achieved. • High-grade calcium phosphates were recovered from the phosphate tailings. • CaHPO 4 and Ca 10 (PO 4) 6 (OH) 2 were obtained at pH 6.0 and 8.0, respectively. [ABSTRACT FROM AUTHOR]

Phosphate tailing is an extremely fine by-product during phosphate ore flotation. Due to the large quantities and relatively higher P 2 O 5 content, the phosphate tailings have been considered as a potential P resource, compared to other P-bearing wastes. Besides, phosphate tailings also contain a large amount of available components, such as Ca, Mg, and Si. To explore a low-cost and efficient process for the utilization of phosphate tailings, the hydrochloric acid leaching-precipitation method was employed to recover phosphorus. The P in phosphate tailings can be selectively dissolved into leaching liquor, followed by the precipitation of calcium phosphates from the leaching liquor through pH adjustment. The results showed that P was predominantly concentrated in fluorapatite and its dissolution ratio increased with the decrease in pH. At pH 1.0, the P dissolution efficiency from phosphate tailings reached 96.3%, along with the majority of Mg and Ca. However, Si was hardly dissolved. It demonstrated that almost all the fluorapatite and dolomite were dissolved while the quartz was difficult to dissolve. Dolomite was more preferentially dissolved than fluorapatite. Increasing temperature contributed to the dissolution of dolomite while suppressing fluorapatite dissolution. The residue containing 87.9% SiO 2 (quartz) and only 0.25% P 2 O 5 has the potential as a building material. As the pH increased to 7.0, the collected precipitate consisted of 34.18% P 2 O 5 and 56.10% CaO, which can serve as a source of a slow-released phosphate fertilizer. The highly efficient utilization of phosphate tailings was achieved via this process. • Selective leaching of P from phosphate tailings can be achieved by HCl solution. • Calcium phosphates are obtained from leachate by the precipitation method. • The obtained precipitate can be used as a slow-released phosphate fertilizer. • The residue mainly composed of quartz has the potential to be a building material. • A method for resource utilization of phosphate tailings was proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • BOF slag and phosphate tailings were synergistically treated to recover P. • P 2 O 5 was concentrated in a specific mineral phase in the synthetic slag. • Selective leaching was applied for separation of the P-rich phase. • Undissolved synthetic slag can be reutilized as a flux in steel plants. • The precipitate extracted from the leachate can be used as a P-Si fertilizer. To efficiently recover phosphorus from industrial solid wastes, the collaborative processing of P-bearing steelmaking slag and phosphate tailings was proposed. Steelmaking slag and phosphate tailings were remelted to make P enrich in a specific mineral phase and then selective leaching was adopted to separate the P-concentrating mineral phase. The P-concentrating leachate can be used to recover calcium phosphate by chemical precipitation. It shows that the P was mainly concentrated in the dicalcium silicate after remelting of steelmaking slag and phosphate tailings and it could be selectively leached. When the mass ratio of the original BOF slag to phosphate tailings was 7:3, the mixed slag with basicity of 2.3 was obtained. The dissolution efficiency of P from this mixed slag reached 89.2% whereas Fe was barely leached at pH 1. The residue containing 68.6% Fe t O and 15.6% MgO can be reused in the metallurgical process. When the pH of leachate was adjusted to 7, more than 89.3% of phosphate ions precipitated in the form of calcium phosphate, and the obtained precipitate containing 28.8% CaO, 19.8% P 2 O 5 , and 47.2% SiO 2 , could be a potential P-Si fertilizer. The total recovery ratio of P from mixed slag was approximately 80% and other components could be reused in steel plants, achieving the comprehensive utilization of steelmaking slag and phosphate tailings. [ABSTRACT FROM AUTHOR]

The electrocoagulation (EC) using metallic Ni foam as electrodes was studied for the removal of boron from solution. The electrolytic parameters were pH (4–12), current density (0.6–2.5 mA cm −2 ), and initial concentration of boron (10–100 mg L −1 ). Experimental results revealed that removal efficiency was maximized at pH 8–9, and decreased as the pH increased beyond that range. At particular onset potentials (0.5–0.8 V vs. Hg/HgO), the micro-granular nickel oxide that was created on the surface of the nickel metal substrate depended on pH, as determined by cyclic voltammetry. Most of the crystallites of the precipitates comprised a mixed phase of β-Ni(OH) 2 , a theophrastite phase, and NiOOH, as revealed by XRD and SEM analyses. A current density of 1.25 mA cm −2 was effective in the EC of boron, and increasing the concentration of boric acid from 10 to 100 mg L −1 did not greatly impair removal efficiency. A kinetic investigation revealed that the reaction followed a pseudo-second order rate model. The optimal conditions under which 99.2% of boron was removed from treated wastewater with 10 mg L −1 -B, leaving less than 0.1 mg L −1 -B in the electrolyte, were pH 8 and 1.25 mA cm −2 for 120 min. [ABSTRACT FROM AUTHOR]

• P and K recovery from actual swine wastewater was found to be feasible. • The maximum recoveries were 97.8% and 69.1% for P and K, respectively. • The recovered K-struvite pellets had low water content (5.5%) and high purity (71.8%). • FBHG recovery can yield a profit of 0.126USD/m3-swine wastewater. The last few decades have seen the critical role of global cattle industry in agricultural development. However, while giving prosperity and significant benefits to the countryside, the industry also produces wastewater streams, that cause eutrophication in water bodies. The streams, if treated effectively, could act as a valuable nonconventional water source to help address the global freshwater crisis. Moreover, resources recovered from these wastewater streams, e.g., potassium (K) and phosphorus (P), could be converted to valuable commodities such as fertilizers. We, therefore, propose to use a continuous K–struvite granulation process as an effective method for the treatment of swine wastewater (SW) and recovery of K–struvite. Results show that the P and K were efficiently removed and that wastewater-derived K–struvite is a promising green chemistry agent for a slow–release, reinforcing a promising pathway to global P and K conservation. The fluidized-bed homogeneous granulation (FBHG) has recently emerged as an advanced metal recovery technology with high efficiencies for several metals and low moisture products. Based on the principle of chemical precipitation, FBHG technology requires less chemicals while producing insignificant amounts of sludge, thereby alleviating burden on sludge management often encountered in conventional chemical precipitation and others. Herein, we investigate the potential use of FBHG technology for simultaneous recovering K and P while treating swine wastewater. The recovered products are in the form of K–struvite pellets having a studded quasi-spherical form with a rough surface and sharp spikes that resemble sea urchins. The pellets are almost free of heavy metals, which make them promising candidates for use as fertilizer without significant harm. We observed that the release of K was faster than that of P. The formation, size, morphology, purity, and crushing strength of the pellets greatly affected the up-flow velocity value condition. The FBHG could potentially be scaled up for more extensive nutrient recovery. [Display omitted] [ABSTRACT FROM AUTHOR]

The fluidized-bed crystallization (FBC) removes heavy metals onto the fluidized pellets, which is an outstanding alternative to the precipitation method. This study simultaneously recovers iron and copper as binary metal-oxide pellets (FeIII 0.66 CuI 0.33 @SiO 2) in a synthetic wastewater using FBC and silica as a seed material. The operating parameters for FBC include the Fe/Cu ratio, pH, cross-sectional loading (L, kg/m2.h) and bed height (H, cm) and these are optimized to maximize the crystallization efficiency of iron and copper. At pH = 8, an input Fe/Cu ratio = 2 at a total metal concentration of 3 mM, the crystallization ratio (CR) and the total respective metal removal (TR) for Fe and Cu is 90% and 99%. Precipitation rates of 0.88 and 0.38 mg-metal/ gr-seed•h were obtained at respective cross-sectional loadings of 0.25 kg m− 2•h and 0.15 kg m− 2•h for Fe and Cu. The crystal phases of FBC product are respectively characterized as FeOOH and Cu 2 O by XRD analysis. The high crystallization ratio and the recovery of crystal pellet product indicated that the quantity of the sludge has been reduced significantly in comparison to the traditional chemical precipitation. [Display omitted] • Mixed metal-containing wastewater was treated by fluidized-bed crystallization. • Fe and Cu were recovered in form of FeOOH/Cu 2 O composite on silica pellet. • 90% of metals were crystallized as oxides as to reduce sludge formation. • Removal efficiency of binary metal oxides achieved 99% under optimal conditions. [ABSTRACT FROM AUTHOR]

Phosphorus is an indispensable nutrient element in agriculture and its reserves are limited. To secure a sustainable supply of phosphorus, phosphate recovery from dephosphorization slag generated in steelmaking was considered a promising solution. In this study, acid leaching was adopted to separate the P-concentrating solid solution from dephosphorization slag. Selective leaching of P from slags with various basicity in the hydrochloric acid solution and chemical precipitation of phosphate ions in the leachate were investigated. Increasing slag basicity facilitated the enrichment of P 2 O 5. Large amounts of Ca, Si, and P were leached from slag, whereas the leaching of Fe was negligible. The leaching efficiency of P increased with slag basicity. At pH 3, the leaching efficiency of P from slag with high basicity reached 96.8% while that of Fe was nearly zero. Almost all the P-concentrating solid solution was dissolved without significant dissolution of the Fe-bearing matrix phase and magnesioferrite. After leaching, the residue containing 57.8% Fe 2 O 3 can be reutilized as a metallurgical feedstock. Through chemical precipitation, a precipitate containing 35.1% P 2 O 5 was recovered from the leachate, which can be used as a phosphate fertilizer. The total recovery efficiency of P from dephosphorization slag in this process reached 95.8%. [Display omitted] • The leaching efficiency of P reached 96.8% without Fe dissolution. • The Fe 2 O 3 -rich residue can be reused as a metallurgical feedstock. • A precipitate containing 35.1% P 2 O 5 was recovered from the leachate. • An efficient method for phosphate recovery from slag was provided. [ABSTRACT FROM AUTHOR]

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, [CO 3 2−] 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. [Display omitted] • High-purity Fe–Cu particles were recovered from wastewater. • A total metal removal of 99% was achieved for both synthetic and real wastewater. • Cost reduction of up to 88% compared to conventional chemical precipitation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sulfide-containing synthetic wastewater was treated by fluidized-bed homogeneous crystallization. • Fluidized bed homogeneous crystallization technology does not need to add the heterogeneous seeds. • The crystallization efficiency of sulfide recovered as zinc sulfide particles reached 97.8%. • Supersaturation is calculated to determine the optimum condition of sulfur crystallization. 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). [ABSTRACT FROM AUTHOR]

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 (L S , kg/m2h) are optimized. The optimum operating conditions of pH 9.8 ± 0.3, [Ni2+] 0 /[S2−] 0 = 0.8, and L S = 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 (NO 3 −, CO 3 2−, PO 4 3−, F−, and Cl−) on the nickel sulfide granulation process was discussed. [Display omitted] • Sulfide wastewater could be treated by FBHC. • The total sulfur removal achieves 95.7%. • The waste cost is 86.0% lower than chemical precipitation. [ABSTRACT FROM AUTHOR]

Abstract This work reports the use of ferrioxalate complexes to assist solar photo-Fenton treatment of pentachlorophenol (PCP) in aqueous medium at mild pH, which inhibits the precipitation of iron hydroxides and allows working at a low iron dosage. The experimental parameters were optimized by assessing the effect of initial concentrations of H 2 O 2 (0–2.5 mM) and Fe(II) (2–10 mg/L), pH (3.0–9.0) and iron/oxalic acid molar ratios (1:0–1:13.5) on total organic carbon (TOC) removal. Ferrioxalate-assisted solar photo-Fenton achieved 97.5% mineralization in 120 min, clearly outperforming conventional Fenton and solar photo-Fenton. The presence of photosensitive ferrioxalate complexes accounted for the enhancement, as a result of Fe(II) regeneration that accelerated the hydroxyl radical (OH) production. The time course of H 2 O 2 and Fe(II) concentrations was evaluated under different iron/oxalic acid ratios. The five carboxylic acids determined by ion-exclusion HPLC and the eight aromatic by-products identified by GC-MS allowed the proposal of a degradation pathway that included hydroxylation, dechlorination and dimerization steps. Complete chloride ion release was achieved after 90 min of treatment. Highlights • Up to 97.5% mineralization achieved by ferrioxalate-assisted solar photo-Fenton process. • Similar TOC abatement was obtained within pH range 3.0–6.0 • Complete dechlorination of PCP at 90 min using low iron dosage (5 mg/L) at pH 5.0 • Fe(III) was maintained soluble, being efficiently reduced to Fe(II) in the presence of oxalate. • Up to 8 aromatic products found by GC-MS: hydroxylation, dechlorination and dimerization. [ABSTRACT FROM AUTHOR]

This work investigated the effective precipitation recovery of boron by chemical oxo-precipitation (COP), which uses hydrogen peroxide (H 2 O 2 ) to transform aqueous boron to easy-precipitating perborates at room temperature. By using barium hydroxide (Ba(OH) 2 ) as a precipitant, the boron removal enhanced with treatment time and the boron level was eventually reduced from 1000 ppm to 3 ppm in four hours. The transformation of the precipitates from amorphous to crystalline was assumed to be responsible for such high boron removal. The aqueous data and the characterization of the precipitates, including elemental analysis, dissolved oxygen, XRD and Raman microscopy, reveal that the phase transformation of perborate species in the precipitates carried out with time during the COP. Mechanisms of COP that describe the precipitates transformation from BaB(OH) 3 OOB(OH) 3 and Ba(B(OH) 3 OOH) 2 to BaB(OH) 2 (OO) 2 B(OH) 2 were proposed. [ABSTRACT FROM AUTHOR]

Chemical oxo-precipitation (COP), which combines treatment with an oxidant and precipitation using metal salts, was developed for treating boron-containing water under milder conditions (room temperature, pH 10) than those of conventional coagulation processes. The concentration of boron compounds was 1000 mg-B L-1. They included boric acid (H3BO3) and perborate (NaBO3). Precipitation using calcium chloride eliminated 80% of the boron from the perborate solution, but was unable to treat boric acid. COP uses hydrogen peroxide (H2O2) to pretreat boric acid, substantially increasing the removal of boron from boric acid solution by chemical precipitation from less than 5% to 80%. Furthermore, of alkaline earth metals, barium ions are the most efficient precipitant, and can increase the 80% boron removal to 98.5% at [H2O2]/[B] and [Ba]/[B] molar ratios of 2 and 1, respectively. The residual boron in the end water of COP contained 15 ppm-B: this value cannot be achieved using conventional coagulation processes. [ABSTRACT FROM AUTHOR]