Dissolution Of CaO Research Articles

Investigation on modified Linz-Donawitz slag for the treatment of Pb2+ ion-laden wastewater - A slag utilization sustainable approach

The present study investigated the adsorptive chemistry of Pb2+ ions eradication using modified Linz-Donawitz slag (LDS), a byproduct of steelmaking industries. The processing of LDS was carried out using a magnetic separation technique followed by planetary micro-crushing. The morphology of surface texture and elemental composition of LDS were examined using SEM and EDS techniques, respectively. XRD and FTIR analysis revealed that the divalent cation of Pb2+ was replaced by Ca2+ to form metal silicate (Pb2SiO4) and ferrite (Pb2Fe2O5) through ion exchange and finally precipitated. The experiment data best fitted Langmuir isotherm and showed excellent adsorption capacity of LDS for Pb2+ adsorption (479 mg/g). Thermodynamic parameters, Gibbs free energy (ΔGo), and enthalpy change (ΔHo) indicated the adsorption was spontaneous and endothermic. The leachability study done by the ICP-OES technique suggested the possibility of immobilizing Ca and Si due to the dissolution of CaO and SiO2. The study demonstrated the potential of LDS for treating Pb2+ ions as part of the waste utilization of the steel industry for a sustainable approach.

Alkaline flux dissociation in blast furnace tuyere bird’s nest: Part 1: CaO dissolution kinetics and slag physicochemical evolution in the coal-coke-slag

In the pursuit of optimizing smelting efficiency and minimizing carbon emissions in blast furnace operations, the strategic introduction of the tuyere alkaline flux injection, particularly in managing the viscosity of the coal-coke-slag in the bird’s nest region, is investigated. This study focused on exploring the dynamics of CaO dissolution within the slag of the coal-coke-slag in the bird’s nest area of a 2200 m3 blast furnace in China, particularly under conditions of instability. Quantitative analysis revealed that at 1550 °C, the CaO maximal dissolution capacity reached 62.05 wt%, with an average rate constant of dissolution observed at 4.65 × 10−4 s−1. The dissolution mechanism was characterized by interfacial dissociation, mass transfer diffusion, and the attainment of a dynamic equilibrium, predominantly influenced by the Ca2+ concentration gradient within the slag. This process facilitates the depolymerization of the slag’s network structure, heavily influenced by the aluminum oxide tetrahedron, effectively reducing slag viscosity. Further, the study quantified the optimal CaO injection content through the tuyere, suggesting a range of 4.00–5.32 kg/tHM, contingent on the use of high-quality raw fuel and advanced high wind temperature technology. This work contributes valuable theoretical insights towards enhancing the efficiency and sustainability of smelting operations, applicable to both conventional and high pellet blast furnaces, marking a significant step forward in the development of low-carbon metallurgical processes.

Dissolution of CaO in SiO2-CaO-Al2O3 Slag in Si Production

This work investigates the dissolution of CaO into three different compositions of SiO2-CaO-Al2O3 slag similar to those found in industrial Si furnaces. It was found that CaO dissolution into the slag is fast. During the dissolution process, a layer containing 35–42% CaO was formed between the CaO particle and the slag, which corresponded to the phases CaO·Al2O3·2SiO2 or 2CaO·Al2O3·SiO2 in this study. Two models were investigated to determine the dissolution rate of the three slags. In the first model, the CaO particle is assumed to be a smooth shrinking sphere, and the rate controlled by the chemical reaction rate. The second model assumes that the rate is controlled by mass transport and depends on the diffusion rate of CaO through a boundary layer on the surface of the CaO. Both models gave similar accuracy to the experimental values, and a proportional relationship between the rate constants and the viscosities was obtained. At 1500 °C, the diffusion coefficients were found to be in the order of 10−6 cm2/s.

Effect of Al Content in Steel on Interfacial Interaction between Molten Steel and MgO Substrate

The apparent contact angles between the molten steel with different [Al] contents (w[Al]) from 0.002% to 0.831% (mass fraction) and the microporous MgO (MM) substrates are measured at 1823 K using the sessile drop method. In particular, the contact angles of No. 1 (w[Al] = 0.002%) and No. 5 (w[Al] = 0.831%) molten steels gradually increase with time at the initial stage. As w[Al] increases from 0.002% to 0.831%, the transformation route of interfacial products between molten steel and the MM substrate is MgO–FeO → MgO·Al2O3 → CaO·2Al2O3 + MgO·Al2O3. The w[Al] of No. 1 molten steel is small, and the dissolution of CaO·ZrO2(s) in the substrate is mainly affected by FeO. As w[Al] increases gradually, [Al] consumes the (MgO) contained in CaO·MgO·SiO2 (CMS), and turns the CMS into (CaO·SiO2) slag layer, which promotes the CaO·ZrO2(s) dissolving and thus increasing the interaction area percentage. When w[Al] is 0.831%, [Al] can react with (CaO·SiO2) slag layer or CaO·ZrO2(s) to form CaO·2Al2O3(s).

Effects of Al2O3/TiO2/Na2O on Lime Dissolution in Steelmaking Slag

The mechanism of lime dissolution in steelmaking slag and the factors that influence the dissolution rate are highly significant in improving the efficiency of the steelmaking process; however, they are yet to be fully understood. Here, the effects of Al2O3/TiO2/Na2O additives on the dissolution rate of lime and the composition of molten slag were investigated using a rotating cylinder technique. The results indicate that the promotion coefficients at 1400 °C decrease in the order of Na2O > TiO2 > Al2O3. Furthermore, the CaO dissolution rate and kinetic parameters were calculated, and the lime dissolution mechanisms in the presence or absence of Al2O3, TiO2, and Na2O were compared. Additionally, the data show that ATN (a mixture with a mass ratio of Al2O3:TiO2:Na2O = 15:4:3) can be used as a suitable flux in the steelmaking process.

Size-dependent dissolution behavior of CaO in the CaO-SiO2-FeO slag system: A molecular dynamics study

In this study, the dissolution behavior of CaO particles of different sizes in CaO-SiO2-FeO slag system was investigated by molecular dynamics simulations. To quantitatively illustrate the dissolution process of the CaO particles in the slag, kullback–leibler divergence was introduced and proven to be a satisfying indicator for the dispersion extent measurement of the added CaO particles in the slag system. The change of oxygen networks and the system potential energies were also analyzed. The results show that the dissolution process of CaO particles with large sizes is longer. When the number of Ca atoms in each CaO particle is smaller than 16, the dissolution process can be neglected. With the addition of CaO in the CaO-SiO2-FeO slag system, bridge oxygen will break and turn into non-bridge oxygen and free oxygen. The homogeneity structure of CaO-SiO2-FeO slag system is barely affected by the added CaO particle sizes. However, the potential energy of the homogeneity system after CaO dissolution is relatively lower when the particle size of the added CaO is small, thus offering a more stable condition for the slag.

Effect of steel slag on ammonia removal and ammonia-oxidizing microorganisms in zeolite-based tidal flow constructed wetlands

The ammonia removal performance of tidal flow constructed wetlands (TFCWs) requires to be improved under high hydraulic loading rates (HLRs). The pH decrease caused by nitrification may adversely affect the NH4+–N removal and ammonia-oxidizing microorganisms (AOMs) of TFCWs. Herein, TFCWs with zeolite (TFCW_Z) and a mixture of zeolite and steel slag (TFCW_S) were built to investigate the influence of steel slag on NH4+-N removal and AOMs. Both TFCWs were operated under short flooding/drying (F/D) cycles and high HLRs (3.13 and 4.69 m3/(m2 d)). The results revealed that a neutral effluent pH (6.98–7.82) was achieved in TFCW_S owing to the CaO dissolution of steel slag. The NH4+-N removal efficiencies in TFCW_S (91.2 ± 5.1%) were much higher than those in TFCW_Z (73.2 ± 7.1%). Total nitrogen (TN) removal was poor in both TFCWs mainly due to the low influent COD/TN. Phosphorus removal in TFCW_S was unsatisfactory because of the short hydraulic retention time. The addition of steel slag stimulated the flourishing AOMs, including Nitrosomonas (ammonia-oxidizing bacteria, AOB), Candidatus_Nitrocosmicus (ammonia-oxidizing archaea, AOA), and comammox Nitrospira, which may be responsible for the better ammonia removal performance in TFCW_S. PICRUSt2 showed that steel slag also enriched the relative abundance of functional genes involved in nitrification (amoCAB, hao, and nxrAB) but inhibited genes related to denitrification (nirK, norB, and nosZ). Quantitative polymerase chain reaction (qPCR) revealed that complete AOB (CAOB) and AOB contributed more to the amoA genes in TFCW_S and TFCW_Z, respectively. Therefore, this study revealed that the dominant AOMs could be significantly changed in zeolite-based TFCW by adding steel slag to regulate the pH in situ, resulting in a more efficient NH4+–N removal performance.

Study on the structural properties of refining slags by molecular dynamics with deep learning potential

The CaO-Al2O3 is the most important basis of the multicomponent slag in the steel making industry. The microstructure of molten CaO-Al2O3 systems affects the physical, chemical, and metallurgic properties of refining slags. It is significant to establish a computational method to accurately describe the microstructure of the slag at the atomic level and speculate the properties of large slag models. In this paper, the effect of compositions on the structure of molten CaO-Al2O3 systems was studied by ab initio molecular dynamics, deep learning theory, and deep potential molecular dynamics. The structures of various molten slags were simulated by ab initio molecular dynamics, which accurately describes the interactions between atoms. The potential functions were obtained by deep learning theory. The properties of the large slag models were simulated by molecular dynamics with deep learning potential. As the molar fraction of CaO increases from 0.5 to 0.7, the combination of O and Al mainly forms [AlO4]-5, [AlO3]-3, and [AlO5]-7. Ca presents mainly as free cations in the molten CaO-Al2O3 system. In addition, the diffusion coefficient of Ca decreases from 9.0 × 10-10 m2/s to 5.4 × 10-10 m2/s. The diffusion coefficients of Al and O slightly decrease and are close to 1.1 × 10-10 m2/s and 3.0 × 10-10 m2/s, respectively. It is deduced that the dissolution of CaO provides free O2– and promotes the formation of [AlOn]-b and increases the polymerization degree, which causes deterioration of the fluidity of molten CaO-Al2O3 slags as XCaO increases from 0.5 to 0.7.

Investigating the active phase of Ca-based glycerol polymerization catalysts: On the importance of calcium glycerolate

Ca-based catalysts are of strong interest for glycerol polymerization reaction due to their high catalytic performances, their wide availability and the absence of any toxicity. In the present study, we investigated the active phase of CaO, Ca(OH)2, CaCO3 and calcium diglyceroxide used as catalysts for this reaction. The solids were analyzed by XRD, solid-state 13C-NMR and TGA-DSC. XRD evidenced the presence of calcium glycerolate in the spent catalysts when CaO, Ca(OH)2 and calcium diglyceroxide were used as starting materials. This was corroborated by the TGA-DSC results. Further, the SS NMR results showed that the as-formed calcium glycerolate is a mixture of linear Ca(C3H7O3) and cyclic-branched Ca(C3H6O3). Moreover, the recycled catalyst issued, e.g., from CaO was more efficient that the initial catalyst with a glycerol conversion of 47 % (vs. 22 % initially for CaO) and a 70 % (vs. 55 %) selectivity to polyglycerols higher than tetraglycerol at 245 °C after 4 h in the presence of 3.5 mol.% of catalyst. As the main outcome, we have shown that Ca-glycerolate is the actual solid active phase, which is formed in situ from CaO and Ca(OH)2 playing the role of catalyst precursors. A mechanism involving the dissolution of CaO and Ca(OH)2, the formation of Ca-glycerolate and its precipitation followed by crystallization, supported by characterization studies, is proposed.

Co-disposal of magnesium slag and high-calcium fly ash as cementitious materials in backfill

Waste minimization is a major approach whereby many industries decrease environmental pollution and promote cleaner production. To achieve sustainable development, a novel idea is proposed herein to recycle magnesium slag (MS) and high-calcium fly ash (FA) into cementitious materials which are then mixed with aeolian sand (AS) to produce a type of paste backfill (MFPB) material that can be used in the mining industry. The rheological and mechanical properties of backfill materials with different FA contents were investigated. The results reveal that: (1) fresh MFPB mortars with different proportions conformed to the Herschel–Bulkley model. The yield stress initially decreased, and then increased with rising FA content. When the FA content was less than 20 wt%, the rheology of the MFPB surpassed that of the pure MS mortar, and an FA content of 10 wt%, yielded the best rheological properties of the fresh MFPB mortar. The mini-slump value, which was between 108 mm (MS-FA0) and 141 mm (MS-FA10), first increased and then decreased with increasing FA content. (2) The unconfined compressive strength (UCS) increased with extended curing times and FA contents, as well as the early-age strength development, which accelerated with increasing FA content. The UCS at 28 d escalated from 2.607 MPa (MS-FA0) to 7.491 MPa (MS-FA40). (3) The microstructure of the MFPB samples was discovered to agree with the UCS results. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) were conducted to investigate the hydration products of the MFPB samples. The hydration mechanism of the MS and FA mixture was discussed, and the former was less reactive when used individually, although its reactivity increased with the addition of high-calcium FA. CaO dissolution in the MS and FA led to the generation of Ca(OH)2, which was a prerequisite for the successive pozzolanic reaction between the MS and FA. This study investigated the feasibility of the co-disposal of MS and FA, which could significantly promote a cleaner mineral production, and mining industry, when used together with backfill technology.

Influence of Al2O3 Level in CaO-SiO2-MgO-Al2O3 Refining Slags on Slag/Magnesia-Doloma Refractory Interactions

The influence of the Al2O3 level in CaO-SiO2-MgO-Al2O3 (CSMA) stainless steel refining slags on the degradation of magnesia-doloma refractories was investigated through static refractory finger corrosion tests. The tests were performed at 1620 °C under Ar atmosphere, using slags with Al2O3 contents of 5, 10, and 20 wt pct, respectively. The results indicate that the formation of 2CaO·SiO2 at the slag/refractory interface was suppressed by increasing the Al2O3 content to 20 wt pct, thereby changing the corrosion mechanism from an indirect dissolution to a direct dissolution of CaO and MgO from the refractories. The increased solubility limit of MgO by the Al2O3-rich CSMA slags results in an overall higher corrosion rate of the MgO-doloma refractory.

The cation-dependent effects of formate salt additives on the strength and microstructure of CaO-activated fly ash binders

This study investigated whether three formate salt additives (Ca(HCOO)2, NaHCOO, and KHCOO) could improve the strength of a CaO-activated fly ash (FA) system. Various tests were conducted to verify the effects of the formate salts including compressive strength, X-ray diffraction (XRD), thermogravimetric (TG) analysis, solid-state 27Al magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and mercury intrusion porosimetry (MIP). The results showed that the addition of Ca(HCOO)2 significantly strengthened the FA binder system by (1) substantially increasing C-S-H formation and (2) measurably reducing overall pore size. However, adding NaHCOO or KHCOO was much less advantageous to strength improvement because although helpful in dissolving FA, the high pH environment caused by their reaction with CaO inhibited further dissolution of CaO, which was the main activator used in this study.

Clarification of the Dissolution of Solid CaO and the Phosphorus‐Enrichment Capability of Calcium Silicates in the Multiphase Slag Based on the Ion and Molecule Coexistence Theory

Recently, a new refining method of using a solid/liquid coexistence multiphase slag for dephosphorization of hot metal was proposed, with the aim to improve the utilization efficiency of CaO and the degree of dephosphorization. Based on this method, an ion and molecule coexistence theory (IMCT) based the thermodynamic model has been developed to clarify the behavior of solid CaO dissolution and the phosphorus‐enrichment capability of calcium silicates in the multi‐phase slag in this article. According to the calculated mass action concentration of the related structural units, the reaction mechanism between solid CaO and the liquid slag in the multi‐phase slag is explained. Meanwhile, the phosphorus‐enrichment capability of calcium silicates is probed. The results show that the dissolution of solid CaO into the multi‐phase slag will be enhanced with the addition of the temperature or the increase of the FeO content, the mass percent ratio of FeO to Fe2O3 (m(FeO)/m(Fe2O3)), and the P2O5 content, while the high basicity (CaO/SiO2) will restrict the dissolution of solid CaO. Besides with the increase of basicity and m(FeO)/m(Fe2O3), the phosphorus‐enrichment contribution ratio of 2CaO · SiO2 displays an exponential growth tendency, while it exhibits an asymmetric parabolic relationship with the increase of FeO, and it slightly decreases with the increase of P2O5 and unchanged with the temperature. Those results obtained can provide a fundamental guidance for the dephosphorization by using the CaO‐based solid/liquid coexistence multiphase slag for hot metal treatment.

Numerical simulations with the P-Hydroslag model to predict phosphorus removal by steel slag filters

The first version of the P-Hydroslag model for numerical simulations of steel slag filters is presented. This model main original feature is the implementation of slag exhaustion behavior, crystal growth and crystal size effect on crystal solubility, and crystal accumulation effect on slag dissolution. The model includes four mineral phases: calcite, monetite, homogeneous hydroxyapatite (constant size and solubility) and heterogeneous hydroxyapatite (increasing size and decreasing solubility). In the proposed model, slag behavior is represented by CaO dissolution kinetic rate and exhaustion equations; while slag dissolution is limited by a diffusion rate through a crystal layer. An experimental test for measurement of exhaustion equations is provided. The model was calibrated with an experimental program made of three phases. Firstly, batch tests with 300 g slag sample in synthetic solutions were conducted for the determination of exhaustion equation. Secondly, a slag filter column test fed with synthetic solution was run for 623 days, divided into 9 cells and sampled at the end of the experiment. Finally, the column was dismantled, sampled and analyzed with XRD, TEM and SEM. Experimental column curves for pH, oPO4, Ca and inorganic carbon were well predicted by the model. Crystal sizes measured by XRD and TEM validated the hypothesis for homogeneous precipitation while SEM observations validated the thin crystal layer hypothesis. A preliminary validation of the model resulted in successful predictions of a steel slag filter longevity fed with real wastewater.

Impact of steel slag on the ammonium adsorption by zeolite and a new configuration of zeolite-steel slag substrate for constructed wetlands.

The CaO dissolution from slag, as well as the effects of influencing parameters (i.e. pH and Ca2+ concentration) on the ammonium adsorption onto zeolite, was systematically studied in this paper. Modeling results of Ca2+ and OH- release from slag indicated that pseudo-second-order reaction had a better fitness than pseudo-first-order reaction. Changing pH value from 7 to 12 resulted in a drastic reduction of the ammonium adsorption capacity on zeolite, from the peak adsorption capacity at pH 7. High Ca2+ concentration in solution also inhibited the adsorption of ammonium onto zeolite. There are two proposed mechanisms for steel slag inhibiting the ammonium adsorption capacity of zeolite. On the one hand, OH- released from steel slag can react with ammonium ions to produce the molecular form of ammonia (NH3·H2O), which would cause the dissociation of NH4+ from zeolite. On the other hand, Ca2+ could replace the NH4+ ions to adhere onto the surface of zeolite. An innovative substrate filling configuration with zeolite placed upstream of the steel slag was then proposed to eliminate the disadvantageous effects of steel slag. Experimental results showed that this novel filling configuration was superior to two other filling configurations in terms of ammonium removal.

Evaluation of thermally-modified calcium-rich attapulgite as a low-cost substrate for rapid phosphorus removal in constructed wetlands

The cost-effective and geographically available substrates are vital for the design of constructed wetlands (CWs), especially the saturated subsurface flow CWs, which are deemed as an efficient way to remove the inlet-lake phosphorus concentrations. In this study, phosphorus removal of thermally-treated calcium-rich attapulgite (TCAP) with varied particle sizes (0.2–0.5 mm, 0.5–1 mm and 1–2 mm) was assessed using batch and long-term column experiments to evaluate its feasibility as a CWs substrate. The phosphorus-bound mechanism in TCAP was identified in various initial phosphorus concentrations. Batch studies indicated that more than 95% of P can be rapidly (<1 h) removed by TCAP from solution with a concentration of 20 mg P/L, and P sorption can be well fitted by a pseudo-second-order equation. The maximum P sorption capacity of TCAP was in the range of 4.46–5.99 mg P/g, and the availability of Ca2+ concentration might limit the P removal capacity of TCAP at high phosphorus concentrations. Both the P removal rate and capacities decreased with the increase of TCAP particle sizes. Column P removal experiments indicated that hydraulic retention time (HRT) exerts great influence on P removal performance and longer HRTs favor the dissolution of CaO in TCAP, consequently increasing the P removal rate. In a 150-day P removal experiment, TCAP removed an average of 93.1%–95.4% of the influent P with a HRT of eight hours. Both the batch and chemical extraction of the P fraction of TCAP showed that the P removed by TCAP was mainly through formation of Ca phosphate precipitation. However, the species of Ca-P precipitation formed might be varied in different phosphorus concentrations. All results indicated that TCAP can be a suitable substrate when used in CWs, and field experiments should be carried out to test its real P removal performance in the future.

Phosphorus Removal from Lake Water Using Basic Oxygen Furnace Slag: System Performance and Characterization of Reaction Products

Effectiveness of basic oxygen furnace slag (BOFS) for removing dissolved phosphorus (P) was evaluated in a hypolimnetic withdrawal system. Lake water collected from the hypolimnion, with phosphate (PO4-P) concentrations of 0.25 to 0.49 mg/L, was passed through a pilot-scale (pore volume, ∼0.87 m3) treatment system over two successive summers. In year 1, the hydraulic retention time (HRT) varied from 0.58 to 1.64 days and 96.1–98.1% PO4-P was removed. The HRT in year 2 was 0.31 to 0.48 days and PO4-P removal was 97.4–99.9%. Effluent pH was 11.37±0.17 and 11.96±0.17 in years 1 and 2, respectively, with the increase attributed to dissolution of CaO and Ca(OH)2 from the BOFS. The effluent was neutralized by addition of CO2(g) before the water was discharged. Vanadium and aluminum were released from the BOFS, and were subsequently removed through addition of a filter containing 5 wt.% granular zero valent iron with a balance of silica sand and by neutralizing pH. Solid phase analyses conducted on the spent media, including FESEM-EDX, XPS, FTIR, and XANES spectroscopy, confirmed the presence of calcium carbonate and calcium phosphate minerals. Diminished hydraulic performance was observed in year 1, which was attributed to CaCO3 accumulation on the spent BOFS media. Restricting ingress of atmospheric CO2 into the system in year 2 minimized the extent of CaCO3 accumulation on the treatment media and led to improved hydraulic characteristics. Results show potential for long-term removal of phosphorus.

CO2 Capture by CaO in Molten CaF2–CaCl2: Optimization of the Process and Cyclability of CO2 Capture

CO2 capture by CaO dissolved or partly dissolved in a molten salt shows high, reversible CO2 sorption because of rapid gas–liquid interactions. Using previously obtained data on CaO reactivity with CO2 in a CaCl2 melt, we describe here the application of the CaF2–CaCl2 molten salt for CaO dissolution or partly dissolution in a CO2 capture process. The effects of the CaO concentration in CaF2–CaCl2 (ratio fixed to the eutectic composition), temperature, and gas composition (CO2–N2) on the carbonation/decarbonation reactions in a one-chamber atmospheric pressure reactor were established by means of a Fourier transform infrared (FTIR) gas detector and gravimetric analysis. The CO2 uptake efficiency by CaO dissolved or partly dissolved in the metal halides was found to enhance and stabilize with concentrations of CaO exceeding 10 wt % in CaF2–CaCl2 in the temperature range of 670–710 °C. Desorption of CO2, performed by a thermal swing technique, proceeded rapidly and completely at 927–946 °C. The CaO activity...

Steel slag filters to upgrade phosphorus removal in small wastewater treatment plants: Removal mechanisms and performance

Electric arc furnace steel slag (EAF-slag) and basic oxygen furnace steel slag (BOF-slag) were used as filter substrate in horizontal subsurface flow laboratory-scale filters designed to remove phosphorus (P) from a synthetic solution (∼10mg P/L). The main objective of this study was to evaluate the influence of various parameters, including slag type, slag size, and slag composition, on P removal performance. Also, a series of chemical and mineralogical analyses was performed to determine the mechanisms of P removal achieved by steel slag in the filters. Over a period of 52 weeks of filter operation, small-size EAF-slag (5–16mm) and small-size BOF-slag (6–12mm) removed 98% and >99% of the inlet total phosphorus (TP), whereas big-size EAF-slag (20–40mm) and big-size BOF-slag (20–50mm) removed 88% and 95% of the influent TP, respectively. The main mechanism of P removal was related to CaO dissolution from slag followed by Ca phosphate precipitation and accumulation of the precipitates into the filters. P removal performance improved with increasing the CaO-slag content and with decreasing slag size, most probably because the specific surface available for CaO dissolution was increased. Also, the experimental results suggested that small-size slag was more efficient than big-size slag for the self-filtration of P precipitates. Chemical and mineralogical analyses indicated that, after precipitation, Ca phosphates may crystallise into the most stable form of hydroxyapatite.

Effects of B&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; and CaF&lt;sub&gt;2&lt;/sub&gt; on Melting Properties of CaO-Based Slags

B2O3 is employed as fluxing agent of CaO-SiO2-Fe2O3 steelmaking slags to substitute for CaF2. The influences of B2O3 and CaF2 on the melting properties of this system slags were investigated and compared. The results indicate that the fluxing effect of B2O3 is more remarkable than that of CaF2. Therefore, B2O3 promotes the dissolution of CaO, SiO2 and 2CaO•SiO2, etc, then the slagging speed can be improved greatly. The melting temperatures of slags increase with the increasing of basicity, especially, when CaF2 is used as fluxing agent as well as the basicity is up to 5.0, the melting temperature is increased higher than 1420°C. These characteristics of boron-containing slgas are more suitable for steelmaking process than those of fluoride-containing slags.