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Chemical oxo-precipitation (COP) is an enhanced precipitation method for boron removal with the conversion of boric acid to perborate anions. When using barium-based precipitant, the boron can be effectively precipitated as barium perborates (BaPBs). The phase transformation of BaPBs from amorphous (A-BaPB, Ba(B(OH) 3 OOH) 2) to crystalline (C–BaPB, BaB 2 (OO) 2 (OH) 4) form is crucial for effective boron removal. However, scaling up this phase transformation of BaPBs is hindered by poor diffusion. This study aims to promote the growth of C–BaPB through seed-induced crystal growth, eliminating the need for phase transformation. By examining the relationship between crystal growth rate and supersaturation, surface spiral growth was identified as the rate-limiting step of the growth of micron-sized seeds near pH pzc. To enable continuous crystal growth, granular seeds of C–BaPB were prepared and employed as the medium for fluidized-bed crystallization (FBC). The system reached steady state 3 hydraulic retention times, achieving 90% boron removal. The effect of surface loading, ionic strength, and dosages on steady-state crystal growth rate was studied, revealing a shift of the rate-limiting step in FBC to diffusion. Lastly, the system that constituted of two FBCs in-series for sequential crystallization of A-BaPB and C–BaPB was demonstrated. The integrated system provided 97.8% of boron removal from synthetic wastewater containing 500 mg-B/L, with 92.3% of boron crystallized on the granular seeds of BaPBs. [Display omitted] • Seed-induced crystal growth of C–BaPB enabled rapid boron removal. • Spiral surface growth was the rate-limiting step near pH pzc. • Continuous crystal growth of granular C–BaPB seeds removed 90% boron in FBC. • Two FBCs in-series eliminated boron from 500 to 8 mg-B/L, >92% on granular seeds. [ABSTRACT FROM AUTHOR]

Atmospheric carbon dioxide (CO 2) imbalance due to anthropogenic emissions has direct impact in climate change. Recent advancements in the mitigation of industrial CO 2 emissions have been brought about by a paradigm shift from mere CO 2 capture onto various adsorbents to CO 2 conversion into high value products. The present study proposes a system which involves the conversion of CO 2 into high purity, low moisture, compact and large CaCO 3 solids through homogeneous granulation in a fluidized-bed reactor (FBR). In the present study, synthetic solutions of potassium carbonate (K 2 CO 3) and calcium hydroxide (Ca(OH) 2) were used as sources of carbonate and precipitant, respectively. The effects of the degree of supersaturation (S) as chemical loading and influx flow rate (Q T) as hydraulic loading on CaCO 3 granulation efficiency were investigated. In the study, S was varied from 10.2 to 10.8 and Q T from 40 to 80 mL min−1 while the operating pH and calcium-is-to-carbonate molar ratio ([Ca2+/[CO 3 2−) were set at 10 ± 0.2 and 1.50, respectively. Results showed that carbonate ions end product distribution had a highest carbonate granulation efficiency at [Carbonate] G of 95–96% using S of 10.6 and Q T of 60 mL min−1. Characterization of the granules confirmed high purity calcium carbonate. Overall, the transformation of industrial CO 2 emissions into a valuable solid product can be a significant move towards the mitigation of climate change from anthropogenic emissions. Image 101088 • Carbon dioxide was recovered by calcium carbonate granulation. • Calcium carbonate removal and granulation efficiencies exceeded 95%. • Effects of supersaturation and cross-sectional loading on granulation were examined. • Physic-chemical characteristics of the recovered granules were analyzed. [ABSTRACT FROM AUTHOR]

The crystallization of struvite in fluidized-bed crystallizer (FBC) was performed to treat synthetic wastewaters that contain phosphorous. Under optimal conditions (pH 9.5, molar ratio Mg/N/P = 1.3/4/1, struvite seed dose (53–297 μm) = 30 g L −1 , total flow rate = 12 ml min −1 , reflux = 120 ml min −1 ), the removal of phosphate (PR) and the crystallization ratio (CR) were 95.8% and 93.5%, respectively. Based on a thermodynamic prediction, the supersaturation, which was obtained from the difference between the theoretical solubility and phosphate concentration, predominated the crystallization efficiency and the properties of the struvite pellets, such as their morphology, particle size and apparent density. Coexisting ions NO 3 − (80, 160 ppm), CH 2 COOH − (260, 520 ppm), F − (650, 1300 ppm) and SO 4 2− (650, 1300 ppm), were utilized to prepare P-containing wastewaters. Of these ions, SO 4 2− (1300 ppm) remarkably reduced the capability of FBC to remove phosphate from solution. In the presence of NO 3 − and CH 3 COO − (for synthesizing TFT-LCD wastewater), and F − and SO 4 2− (for synthesizing semiconductor wastewater), CR% was lower than in pure water, although the ultimate PR% did not differ significantly. [ABSTRACT FROM AUTHOR]

Heavy metal removal is a significant task that protects our water resources. Fluidized-bed homogeneous granulation process (FBHGP) was used to treat nickel containing wastewaters by recovering nickel in the form of nickel carbonate hydroxide granules with low moisture content rather than soft sludge. This study investigated nickel removal and recovery through HFBGP by determining the effects of varying influent nickel concentrations, [CO 3 2− : Ni 2+ ] molar ratios, and pH of the precipitant. This was conducted in a continuous process using a laboratory scale fluidized-bed reactor that determined the effects driven by supersaturation. The best operating conditions that resulted in a 98.8% nickel removal and 97.8% granulation efficiency were 200 mg L −1 influent nickel concentration, 2.0 M R of [CO 3 −2 :Ni +2 ], and 10.7 pH of precipitant. Based on SEM analysis, the granules formed have sizes between 0.50 mm and 0.15 mm. EDS results showed that the atomic percentages of nickel carbon, and hydrogen were ∼50%, ∼9–12%, and ∼35% respectively, representing the nickel carbonate compound. The XRD results showed the low symmetry of the granules formed that confirmed the characteristics of nullaginite mineral of Ni 2 (CO 3 )(OH) 2 . [ABSTRACT FROM AUTHOR]