赤泥-煤矸石协同还原焙烧回收Fe、Al有价元素

赤泥和煤矸石是典型的铝硅酸类固体废物,两者协同还原焙烧有助于实现其所含Fe、Al等有价元素的回收。采用热力学计算、热重分析、X射线衍射分析、电感耦合等离子体发射光谱分析等方法,考察了赤泥-煤矸石协同还原焙烧过程中,焙烧温度、焙烧时间、赤泥-煤矸石质量比对还原焙烧产物物相组成及其所含Fe、Al等有价元素回收效率的影响。结果表明,混合物料中铝硅酸盐物相和含铁物相随焙烧温度的升高呈现规律性变化,如高岭石相转变规律为,高岭石→偏高岭石;钙霞石相转变规律为,钙霞石→钙黄长石;水化石榴石相转变规律为,水化石榴石→铝酸钙;赤铁矿依次转变为,Fe₂O₃(非磁性)→Fe₃O₄(磁性)→FeO(非磁性)→Fe(磁性)。当焙烧温度为600 ℃、焙烧时间为60 min、赤泥-煤矸石质量比为7:3时,铁精矿产出率为15.6%、铁品位达55.6%、Al溶出率为73.6%。在此基础上,建立了“赤泥-煤矸石协同还原焙烧-磁选-酸浸”的工艺,可实现煤矸石、赤泥中Fe、Al等有价元素的同步回收。     

Dissolution behavior of representative elements from red mud (RM) by leaching with titanium white waste acid (TWWA)

Titanium white waste acid (TWWA) was used to dissolve the representative elements from red mud (RM) to achieve the goal of “treating waste with waste.” The leaching parameters on the leaching efficiency of Na, Sc, and Al were investigated, in which the analysis of XRD and SEM–EDS on RM and leaching residue was performed. The leaching kinetics of Na, Sc, and Al was studied with unreacted shrinking core model (USCM). The results show that the dealkalization efficiency was close to 100%, and the leaching efficiency of Sc and Al was 82% and 75%, respectively. Cancrinite was dissolved from RM, and then the elements such as Na, Al, and Ca reacted with H₂SO₄ of TWWA. Na existed in the leaching liquor in the form of ions. Ca reacted with sulfuric acid to form anhydrite, which existed in the leaching residue. The particles of RM became smaller and dispersed with each other by acid leaching. The leaching apparent activation energy of Na, Sc, and Al was 4.947 kJ/mol, 6.361 kJ/mol, and 31.666 kJ/mol, respectively. The leaching kinetic equation of Na, Sc, and Al was 1???(1???a)^2/3?=?0.084·exp[??595.05/T]·t by external diffusion, 1???2a/3???(1???a)^2/3?=?0.021·exp[??765.16/T]·t by internal diffusion, and ln(1???a)/3?+?(1???a)^?2/3 – 1?=?67.12·exp[??3808.8/T]·t by joint action, respectively.

     

盐酸浸出提取赤泥中铝和铁的工艺条件优化

系统研究盐酸浸出赤泥中铝和铁的过程,考察酸浸温度、盐酸浓度、酸浸时间、液固比以及赤泥粒度对铝、铁浸出率的影响。单因素实验和正交实验结果得出,在影响浸出率的酸浸温度、盐酸浓度、酸浸时间和液固比对铁、铝的浸出率的影响几个因素中,酸浸温度和盐酸浓度的影响最大,液固比和浸出时间其次。盐酸酸浸的最佳工艺条件为：赤泥粒度150 μm、酸浸温度80 ℃、盐酸浓度10 mol·L-1、液固比8∶1（V/m）、浸出时间150 min,此时铝的浸出率为96.7%,铁的浸出率为95.1%,铁铝总浸出率96.0%。     

Speciation of rare earth elements in soil and accumulation by wheat with rare earth fertilizer application

A greenhouse study was conducted to investigate the accumulation of rare earth elements (REEs), La, Ce, Pr and Nd, in winter wheat (Triticum aestivum L.), and the speciation of these elements in soil following the application of REE-based fertilizers. Improved crop yield was confirmed by the experiment. The accumulation behavior of La, Ce, Pr and Nd in wheat varied depending on the concentration of REE fertilizer application, i.e. increased with increasing REE concentration at low fertilization application, constant over the medium REE range, and decreased with increasing REE concentration at high fertilizer application. Significant negative correlation was obtained between REE contents in roots and soil pH (r = -0.5787 to -0.8442 for La). REEs in both the fertilized and unfertilized soils were fractionated by a three-stage sequential extraction procedure into three chemically distinct fractions: water soluble, exchangeable and carbonate bound (B1), Fe-Mn oxide bound (B2), and organic and sulfide bound (B3). REEs in fertilized soils were found mainly in the B2 and B3 fractions, with only a small amount in the B1 fraction. REEs in B1 and B2 fractions were negatively correlated with soil pH (r = -0.6892 to -0.8927 and -0.7462 to -0.9482). Significant correlation was obtained between REEs in B1 fraction and REE contents in root. The correlation coefficients ranged from 0.6159 to 0.7410 when fertilizer application was lower than 20.0 mg/kg soil. No acceptable relationship was observed between REE contents in shoot and any of the extractable fractions in soils.     

Assessment of the bioavailability of rare earth elements in soils by chemical fractionation and multiple regression analysis

The bioavailability of rare earth elements (REEs) in soils was evaluated, based on the combination of chemical fractionation and multiple regression analysis. REEs in soils were partitioned by a sequential extraction procedure into water soluble (F(ws)), exchangeable (F(ec)), bound to carbonates (F(cb)), bound to organic matter (F(om)), bound to Fe-Mn oxides (F(fm)) and residual (F(rd)) fractions. Alfalfa (Medicago Staiva Linn.) had been grown on the soils in a pot-culture experiment under greenhouse conditions for 35 days. The concentrations of REEs in fractions and plant were determined by inductively coupled plasma-mass spectrometry (ICP-MS). Chemical fractionation showed that (F(ws)) fraction of REEs was less than 0.1% and residual (F(rd)) was the dominant form, more than 60% in soils. Bioaccumulation of REEs was observed in Alfalfa. REE availability to the plant was evaluated by multiple regression analysis. F(ws), F(ec), F(cb) and F(om) fractions were significantly correlated with REE uptake by alfalfa. But the exchangeable Pr(F(ec)) was significantly correlated with Pr concentration in alfalfa. F(ec), F(cb) and F(om) greatly contributed to La and Nd bioavailability; F(ec) and F(om) to Ce, Gd and Dy; F(ec) and F(cb) to Yb; and F(ws), F(ec) and F(om) to total REEs. This meant that the bioavailability of different species of REEs varied with individual REE. The results of this study indicated that the sequential extraction procedure, in conjunction with multiple regression analysis, may be useful for the prediction of plant uptake of REEs from soils.     

Effects of soil type on leaching and runoff transport of rare earth elements and phosphorous in laboratory experiments

Introduction  

Through leaching experiments and simulated rainfall experiments, characteristics of vertical leaching of exogenous rare earth elements (REEs) and phosphorus (P) and their losses with surface runoff during simulated rainfall in different types of soils (terra nera soil, cinnamon soil, red soil, loess soil, and purple soil) were investigated.     

Effects of redox potential and pH value on the release of rare earth elements from soil

Equilibrium release experiments were conducted under three different pH values of 3.5, 5.5 and 7.5 as well as three redox potentials of 400, 0 and -100 Mv to investigate the influence of redox potential and pH value on the La, Ce, Gd and Y release of from the simulated-REEs-accumulation (SRA) soil. Oxygen and nitrogen were allowed to flow into soil suspension to adjust redox potential to a preset value, and 1 mol/l HCl or 1 mol/l NaOH solutions were added into the soil suspension to keep pH at a preset value. Results indicated that La, Ce, Gd and Y release increased gradually with the decrease of pH value or Eh, and the influence of redox potential on Ce was more remarkable than on La, Gd and Y. At the same time. It was observed that La, Ce, Gd and Y releases were positively correlated with the release of Fe and Mn, indicating that La, Ce, Gd and Y releases might originate from dissolution of Fe-Mn oxyhydroxides under reduction and low pH conditions. Moreover, it was found that alteration of pH value and redox potential might affect the change of La, Ce, Gd and Y species in the soil. The contents of La, Ce, Gd and Y in exchangeable fraction and Fe-Mn oxide fraction in the solid phase from soil suspension separation decreased with the decline of pH value and redox potential. Multiple stepwise regression analysis showed that exchangeable fraction and Fe-Mn oxide fraction predominately contributed to the La, Ce, Gd and Y release. Low pH value and redox potential were more favorable to La, Ce, Gd and Y releases following the change of their species. The La, Ce, Gd and Y contents in exchangeable fraction and Fe-Mn oxide fraction are the main contributors to their release.     

Analysis of essential,toxic, rare earth,and noble elements in maternal and umbilical cord blood

Environmental Science and Pollution Research - Progressive industrialization in recent decades has contributed to the increase of metal levels in the environment, which has a dangerous impact on...     

Emission inventory of eight elements,Fe, Al,K, Mg,Mn, Na,Ca and Ti,in dust source region of East Asia

Based on calculation of the emission rate of the atmospheric mineral dust and the data of elemental contents in surface soils, this paper calculates the emission inventory of eight main elements of the atmospheric dust, Fe, Al, K, Mg, Mn, Na, Ca and Ti, in the dust source region of East Asia. As the dust sources in both Northern China and the Southern Mongolia are of three types and, in each of the six source type areas, surface soils are relatively uniform in soil types and soil texture, a simple method to calculate the emission of an element in one source type area is proposed by multiplying the total emission of the dust PM₁₀ and PM₅₀ in the source type area with the mean percentage content of the element in surface soils of the area. Comparison of our calculation of the total Fe emission in the source region of East Asia with the total Fe deposition to the North Pacific Ocean, measured and calculated by previous authors, shows very good agreement. This general method can also be used for the emission calculation of any other element.     

Enhanced Fenton removal of phenol catalyzed by a modified red mud derived from the reduction of oxalic acid and l-ascorbic acid

Environmental Science and Pollution Research - Red mud, a bauxite residue generated during alumina production through the Bayer process, contains oxides of Fe, Ti, Al, Mn, and rare earths, and has...     

Bioaccumulation of the rare earth elements lanthanum, gadolinium and yttrium in carp (Cyprinus carpio)

Widespread use of the rare earth elements (REEs) in China for agricultural purposes, together with many other applications, has resulted in a remarkable increase of REE concentrations in the environment. The comparative bioaccumulations of representative light, medium and heavy REEs in a variety of tissues of carp (Cyprinus carpio L.) were investigated for an evaluation of their impacts on aquatic animals. The fish were exposed continuously to solutions containing 0.50 mg litre(-1) of each element for 45 days at pH 6.0 and sacrificed at time intervals. Skeleton, muscle, gills and internal organs were analysed for REE contents. A method using cation-exchange resin separation and ICP-AES determination was developed for the quatification of individual REEs. The results show that carp has low ability to take up the REEs under the experimental conditions. The order of REEs under the experimental conditions. The order of maximum bioconcentration factors was mostly internal organs > gills > skeleton > muscle. Neither synergistic nor antagonistic effects of the mixed REE solutions for carp were observed. The relative distributions of different REEs in the investigated tissues exhibited similar patterns. Among the selected tissues studied, the concentration of a heavy REE (Y) was the smallest, while concentrations of a medium (Gd) and a light REE (La) showed only a slight difference.     

Geochemical characteristics of dissolved rare earth elements in acid mine drainage from abandoned high-As coal mining area,southwestern China

Acid mine drainage (AMD) represents a major source of water pollution in the small watershed of Xingren coalfield in southwestern Guizhou Province. A detailed geochemical study was performed to investigate the origin, distribution, and migration of REEs by determining the concentrations of REEs and major solutes in AMD samples, concentrations of REEs in coal, bedrocks, and sediment samples, and modeling REEs aqueous species. The results highlighted that all water samples collected in the mining area are identified as low pH, high concentrations of Fe, Al, SO₄ ^2? and distinctive As and REEs. The spatial distributions of REEs showed a peak in where it is nearby the location of discharging of AMD, and then decrease significantly with distance away from the mining areas. Lots of labile REEs have an origin of coal and bedrocks, whereas the acid produced by the oxidation of pyrite is a prerequisite to cause the dissolution of coal and bedrocks, and then promoting REEs release in AMD. The North American Shale Composite (NASC)-normalized REE patterns of coal and bedrocks are enriched in light REEs (LREEs) and middle REEs (MREEs) relative to heavy REEs (HREEs). Contrary to these solid samples, AMD samples showed slightly enrichment of MREEs compared with LREEs and HREEs. This behavior implied that REEs probably fractionate during acid leaching, dissolution of bedrocks, and subsequent transport, so that the MREEs is primarily enriched in AMD samples. Calculation of REEs inorganic species for AMD demonstrated that sulfate complexes (Ln(SO₄)⁺and Ln(SO₄)₂ ^?) predominate in these species, accounting for most of proportions for the total REEs species. The high concentrations of dissolved SO₄ ^2? and low pH play a decisive role in controlling the presence of REEs in AMD, as these conditions are necessary for formation of stable REEs-sulfate complexes in current study. The migration and transportation of REEs in AMD are more likely constrained by adsorption and co-precipitation of Fe-Al hydroxides/hydroxysulfate. In addition, the MREEs is preferentially captured by poorly crystalline Fe-Al hydroxides/hydroxysulfate, which favors that sediments also preserve NASC-normalized patterns with MREEs enrichment in the stream.

     

Provenances of atmospheric dust over Korea from Sr–Nd isotopes and rare earth elements in early 2006

Sr and Nd isotopic composition of pre- and syn-Asian dust (Hwangsa) particles collected from three different water depths at two different offshore sites, western Korea and rare earth elemental composition of syn-Asian dust particles collected from three islands around the Korean Peninsula in late April 2006 were analyzed to interpret their provenance. The dust Sr–Nd isotopic compositions vary spatiotemporally, but they show specific values when the Hwangsa event occurred. Satellite images, airmass backward trajectory modeling, and comparison with Sr–Nd isotopic ratios and rare earth elements compositions of soils and desert sands of northern China all suggest the major source of dust particles for the late April 2006 Hwangsa event to be the Mu Us Desert in northern China. Dust particles of the pre-Hwangsa period include both background dusts and the previous Hwangsa event dust particles, and they are interpreted to have been originated from various arid regions of China such as the Hobq Desert, the Mu Us Desert, and the Taklamakan Desert in different times. Different background dust sources during pre-Hwangsa period in early 2006 resulted from the changing route of the westerlies.     

A human health risk assessment of rare earth elements in soil and vegetables from a mining area in Fujian Province,Southeast China

Contaminated food through dietary intake has become the main potential risk impacts on human health. This study investigated concentrations of rare earth elements (REEs) in soil, vegetables, human hair and blood, and assessed human health risk through vegetables consumption in the vicinity of a large-scale mining area located in Hetian Town of Changting County, Fujian Province, Southeast China. The results of the study included the following mean concentrations for total and bio-available REEs of 242.92 ± 68.98 (135.85–327.56) μg g⁻¹ and 118.59 ± 38.49 (57.89–158.96) μg g⁻¹ dry weight (dw) in agricultural soil, respectively, and total REEs of 3.58 ± 5.28 (0.07–64.42) μg g⁻¹ dw in vegetable samples. Concentrations of total REEs in blood and hair collected from the local residents ranged from 424.76 to 1274.80 μg L⁻¹ with an average of 689.74 ± 254.25 μg L⁻¹ and from 0.06 to 1.59 μg g⁻¹ with an average of 0.48 ± 0.59 μg g⁻¹ of the study, respectively. In addition, a significant correlation was observed between REEs in blood and corresponding soil samples (R² = 0.6556, p < 0.05), however there was no correlation between REEs in hair and corresponding soils (p > 0.05). Mean concentrations of REEs of 2.85 (0.59–10.24) μg L⁻¹ in well water from the local households was 53-fold than that in the drinking water of Fuzhou city (0.054 μg L⁻¹). The health risk assessment indicated that vegetable consumption would not result in exceeding the safe values of estimate daily intake (EDI) REEs (100−110 μg kg⁻¹ d⁻¹) for adults and children, but attention should be paid to monitoring human beings health in such rare earth mining areas due to long-term exposure to high dose REEs from food consumptions.     

Distribution of selected heavy metals and rare earth elements in surficial sediments from the polish sector of the Vistula Lagoon

The concentrations of 22 trace elements plus the rare earth elements (REE) were determined in the <63 μm fraction of surficial sediments from the Polish sector of the Vistula Lagoon by ICP-MS. For the anthropogenically-enriched elements, the mean element enrichment factors (EF's) decrease in the sequence Ag (9.9) > Sb (7.5) >As (5.8) ≥ Cd (5.2) > Pb (3.7), albeit with large variability in concentration in the sediments from one station to another. These observations demonstrate that sediments from the Vistula Lagoon are locally polluted by these anthropogenically-derived elements. Plots of NASC-normalized REE data show that the REE patterns of the sediments have not been significantly modified during transport from their source with only a minor depletion of the heavy rare earth elements (HUE) compare to the light rare earth elements (LREE). The lack of any significant anomalies for Ce and Eu indicates that redox processes have not played a major role in modifying the distribution of the REE. Factor ananalysis of the compositional data shows that sediments from the Polish sector of the Vistula Lagoon can be divided into three main groups depending on the geographical location and the degree of contamination by heavy metals.     

Assessing the chemical behavior and spatial distribution of yttrium and rare earth elements (YREEs) in a coastal aquifer adjacent to the Urmia Hypersaline Lake,NW Iran

This study aims to shed light on the seasonal behavior of yttrium and rare earth elements (YREEs) in the Urmia Aquifer (UA), in the immediate vicinity of Urmia Lake (UL) in Iran. Samples of groundwater, collected under dry and wet conditions in coastal wells of UA, suggest a large degree of variability in both YREE abundance and normalized patterns. Although weathering or water-rock interactions (between the surface/groundwater and rock samples) were predicted to be the most probable source in explaining YREEs in groundwater samples, results to the contrary indicate that the groundwater do not inherit aquifer rock-like YREE signatures in the study area; this might be due to the relative stability of YREEs during the process of water-rock interactions, which suggest that methods based on YREEs can be beneficial in discrimination of water sources. Furthermore, findings demonstrated no significant relationship between Ce/Ce* and salinity (0.08 and 0.05 in wet and dry seasons, respectively), and between Eu/Eu* and salinity (0.1 and ?0.04 in wet and dry seasons, respectively). Dissimilarity of patterns of YREEs in rock and water samples reveals YREEs as no conservative tracers in determining the UL saltwater intrusion into coastal groundwater. Therefore, the groundwater YREE concentrations and fractionation patterns in UA warrant controlling by coastal aquifer need to be controlled by other chemical weathering, adsorption, desorption, and solution complexation reactions. Finally, comparison of REE concentration values in groundwater samples with corresponding indicative admissible drinking water concentrations (IAC) demonstrated their suitability for drinking purposes.

     

铝铁电极联用电絮凝法处理Cu-EDTA络合废水

采用电絮凝法处理Cu-EDTA模拟废水,研究电极组合方式、初始pH值和氯化钠浓度3个因素对化学需氧量(COD)和Cu去除效果的影响。实验研究发现,当电极组合方式为2个铝阳极和2个铁阴极,起始pH值为3,氯化钠浓度为0.5 g/L,换极周期为40 min,反应时间为80 min时,COD去除率达到78.7%,Cu离子去除率达到99.9%。通过实验研究确定EDTA的去除机制主要是:酸性条件下的次氯酸氧化作用,碱性条件下的氢氧化物絮凝沉淀作用及单核态铝/铁与多核态铝/铁电荷中和作用,Cu的去除机制主要是氢氧化物的絮凝沉淀作用和铁电极的电沉积作用。     

Physical,chemical, and mechanical properties of landfilled waste from Campina Grande,Brazil

Environmental Science and Pollution Research - The properties of municipal solid waste (MSW) in landfills vary considerably, depending on the waste’s composition, time, and density. This...