Leaching Of Zn Research Articles

Forest floor leachate fluxes under six different tree species on a metal contaminated site

Trees play an important role in the biogeochemical cycling of metals, although the influence of different tree species on the mobilization of metals is not yet clear. This study examined effects of six tree species on fluxes of Cd, Zn, DOC, H+ and base cations in forest floor leachates on a metal polluted site in Belgium. Forest floor leachates were sampled with zero-tension lysimeters in a 12-year-old post-agricultural forest on a sandy soil. The tree species included were silver birch (Betula pendula), oak (Quercus robur and Q. petraea), black locust (Robinia pseudoacacia), aspen (Populus tremula), Scots pine (Pinus sylvestris) and Douglas fir (Pseudotsuga menziesii). We show that total Cd fluxes in forest floor leachate under aspen were slightly higher than those in the other species' leachates, yet the relative differences between the species were considerably smaller when looking at dissolved Cd fluxes. The latter was probably caused by extremely low H+ amounts leaching from aspen's forest floor. No tree species effect was found for Zn leachate fluxes. We expected higher metal leachate fluxes under aspen as its leaf litter was significantly contaminated with Cd and Zn. We propose that the low amounts of Cd and Zn leaching under aspen's forest floor were possibly caused by high activity of soil biota, for example burrowing earthworms. Furthermore, our results reveal that Scots pine and oak were characterized by high H+ and DOC fluxes as well as low base cation fluxes in their forest floor leachates, implying that those species might enhance metal mobilization in the soil profile and thus bear a potential risk for belowground metal dispersion.

Bioavailability and leachability of heavy metals during water hyacinth composting

The bioavailability and leachability of heavy metals is important role when considering their toxicity during composting following land application. Therefore, studies were carried out on Zn, Cu, Mn, Fe, Ni, Pb, Cd and Cr during 30 days agitated-pile composting of water hyacinth (Eichhornia crassipes). This study investigated the influence of parameters such as pH, temperature and organic matter content on the distribution of heavy metal bioavailability and leachability during composting of water hyacinth. Results showed that the contents of total metal concentration increased during the composting process. The bioavailability of heavy metals was investigated in the form of water soluble and diethylene triamine pentaacetic acid (DTPA) extractable. In the water soluble, DTPA and leachable Zn, Cu, Mn, Ni and Cr reduced but there was a gradual increase in the Fe concentration during the composting process. Furthermore, in water soluble and leachable Ni, Cd and Pb were not detected and in DTPA extractable Cd and Pb were also not detected during 30 days of composting.

Fate and behaviour of Cu and Zn from pig slurry spreading in a tropical water–soil–plant system

Pig slurry is commonly spread on crop fields as a means of managing this agricultural waste product. However, this practice has an impact on the environment, e.g. increasing soil copper (Cu) and zinc (Zn) concentrations. Many studies have assessed the fate of these elements, but some questions remain, especially with respect to tropical agrosystems which have yet to be studied in depth. The aim of this study was to determine the fate of Cu and Zn from pig slurry spreading while also focusing on describing the dynamics of these elements in a tropical system and accounting for the three compartments of the water–soil–plant system. We observed that all of the Zn accumulated within the 20–60cm soil layer. Although the uncertainty calculated for these results was high, these findings were confirmed by the absence of uptake by the plant cover and of leaching via water flows. This pattern for Zn in a tropical setting differed from findings generally reported in temperate areas. The Zn accumulation mechanism in tropical soil seems to be a reversible sorption phenomenon, suggesting the possibility of long-term Zn leaching. The Cu mass derived from pig slurry spreading was stored in the 0–20cm soil layer. This result obtained in a tropical environment was similar to that noted in temperate areas. This could be explained by Cu speciation in the pig slurry (insoluble copper sulfide), and was therefore relatively independent of the soil–climate system.

Leaching of zinc from calcined smithsonite using sodium hydroxide

The processes of calcination and alkaline leaching were applied to treat a zinc oxide ore, smithsonite (ZnCO3). The phase evolution in the calcination was studied, as well as the effect factors on the leaching rate of Zn, such as calcination temperature, alkaline concentration, phase ratio of liquid to solid (L/S), leaching temperature and leaching time. It was found that the ZnCO3 had completely decomposed into ZnO when calcined for 2h at 400°C and the Zn leaching rate of ores calcined at 400°C could be over 92% with 20% (6.25mol/L) sodium hydroxide and a phase ratio of 80:1 for 4h at 100°C.

Investigation and modelling of the progression of zinc leaching from large sphalerite ore particles

X-ray Computed Tomography (CT) was used to follow the progression of Zn leaching in a number of individual sphalerite ore particles, which were subjected to a long-term simulated heap bioleaching environment. The ore was prepared by two different modes of comminution – HPGR at 90bar and cone crusher – and individual particles were selected from three different size fractions. Investigation of the reacted fraction of Zn vs distance from the centre of each particle indicated that leaching from large particles leads to near complete conversion near the surface, but only partial conversion in the zones that are closer to the centre of particles. The cores of the cone-crushed particles show hardly any conversion at all, especially in the larger particle sizes.Mathematical analysis shows that leaching from the large particle does not follow the shrinking core model. It is shown that the progression can rather be described by a combined reaction–diffusion process progressing through the network of cracks and pores closer to the particle surface. Extent and depth of this network are a function of particle size and comminution method. A simplified rate model is proposed that describes the extent of leaching as a function of time in terms of a set of parameters that can all be related to just particle size and crushing mode.

Comparison of potentially toxic metals leaching from weathered rocks at a closed mine site between laboratory columns and field observation

Abstract Potentially toxic metals, such as Cu, Pb and Zn, are leached from weathered rocks at many closed mine sites due to the acidic environments and mineralogical modifications. The mobilized toxic metals may cause contamination of surrounding water bodies. In this study, both laboratory column experiments and field observations at a former mine located in the north of Japan were carried out to compare the leaching behavior of Cu, Pb and Zn. The thickness of the surface weathered rock was varied (10, 20 and 30 cm) for the columns experiments while porous cups for porewater sampling were set up at different depths (GL-15, -45, -70, and -95 cm) for the field observations. Deionized water was added once a week over 75 weeks to the columns to simulate rainfall while porewater was extracted by a vacuum pump in several sampling campaigns (over 18 months). Similar low pH and leaching behavior of potentially toxic metals were observed for column experiments and field observations. A moderate increase in concentration with depth was observed for Cu and Zn. However, no increase in concentration was observed for Pb. This suggests that the leaching of Cu and Zn is enhanced by the length of the flow pathway through the weathered rock layer while Pb concentration is restricted by the precipitation of insoluble Pb sulfate. Thus, the thickness of the weathered rock layer is an important parameter that should be taken into consideration to estimate the loads of some potentially toxic metals, which is important when designing remediation schemes.

Bioleaching of heavy metals from sewage sludge using indigenous iron-oxidizing microorganisms

The objective of this study was to investigate the bioleaching of Cr, Cu, Pb, and Zn from sewage sludge using iron-oxidizing microorganisms. These conditions include the solid concentration, initial pH, ferrous iron concentration, inoculum concentration as well as the kinetics of solubilization of metals from sewage sludge to determine whether they impact on bioleaching efficiency. The sludge sample containing bacteria used in this study was collected from Fuzhou Jingshan sewage treatment plant. Indigenous iron-oxidizing bacteria were enriched from the sludge. Conditions affecting the bioleaching and application were conducted using batch experiments. The analysis of Cr, Cu, Pb, and Zn was carried out with an atomic absorption spectrophotometer, and the pH and ORP were measured using pH meter and ORP meter. The data show that 88.5 % of Zn, 79.9 % of Cu, 50.1 % of Pb, and 33.2 % of Cr can be removed from the sludge after 12 days of bioleaching at 30 °C, while only 80.2 % of Zn, 21.8 % of Cu, 10.9 % of Pb, and 10.5 % of Cr were leached out in the control without iron-oxidizing microorganisms. The leaching kinetics study shows that the rate of metal solubilization in bioleaching using iron-oxidizing microorganisms was more effective compared to chemical leaching. The results suggest that the leaching of metals from sludge can be attributed to two leaching approaches: firstly, chemical leaching; and secondly, bioleaching. However, their effectiveness depends on metal species because of their different bindings in sludge. For example, the leaching of Zn from the sludge was dominated by chemical leaching while the removal of Cu, Pb, and Cr was dominated by bioleaching.

Biosolid and distillery effluent amendments to Irish short rotation coppiced willow plantations: Impacts on groundwater quality and soil

The impact of landspreading organic byproduct (OB) on the quality of groundwater (GW) and soil underlying short rotation coppiced willow plantations was assessed. Organic byproduct, namely biosolid (BS) and distillery effluent (DE), was spread on six plots (each with a plot area of 0.059ha) at OB treatment-rates of 100%, 50% and 0%. The OB treatment rate was defined by the maximum permissible soil-P load defined in Irish regulation. Groundwater was sampled each month and tested for pH, electrical conductivity (EC), NO3, PO43, total soluble phosphorous (TSP), K and six heavy metals (HMs) Cu, Cd, Cr, Pb, Ni, and Zn. Results were assessed in relation to Irish GW threshold values (GTVs), to assess overall quality using a “well bottom” approach. The background concentration of GW K and GW P (established in early 2008, prior to all OB spreading) were above permissible Irish statutory limits, in all cases. There was evidence of percolation of K and TSP to GW; K and PO43 concentrations breached GTVs across all plots. There was also evidence of percolation of Cu through soil profile, though Cu GW concentration did not breach GTV, and no risk to GW quality is necessarily implied. A potential (though small) risk of P- and K-percolation could impact GW quality in commercially scaled-up plantations; however, risk to GW quality from NO3, Cu, Cd, Cr, Pb, Ni, and Zn leaching in soil are minimal. Sites considered for energy crop should be assessed for soil conditions, and vulnerability to leaching, before OB amendment programs are initiated. The study was conducted over two years; the longer term impact of applications of BS and DE on soil organic-matter content, salinity and pH (and subsequent loss through soil profile) should be assessed. The implication of scaling up test-bed sized applications to larger commercial plantation scales needs to be considered.Capsule: Amendments of organic byproduct to short rotation coppice willow may lead to leaching of nutrients to groundwater in certain circumstances.

POSSIBILITY OF USING WASTE PAINTING POWDER FOR METAL SURFACE FINISHING SLUDGE STABILIZATION

The process of powder coating produces two kinds of waste: metal surfaces finishing sludge and waste painting powder. Before disposal, waste painting powder is sintered and converted into a solid mass. This work investigated the possibility of using waste painting powder for metal surface finishing (phosphating) sludge stabilization. Tests for heavy metal leaching from three different phosphating sludges and from sintered samples were carried out. The content of hexane soluble substances in the sludge and in the stabilized samples was also tested. The investigation has shown that waste painting powder sintering is not suitable for metal finishing sludge stabilization since due to this method the leachability of Zn was reduced by 67%, Fe – 54%, and Cu – just by 42%. DOI: http://dx.doi.org/10.5755/j01.ct.60.2.1718

Effects of sewage sludge biochar on plant metal availability after application to a Mediterranean soil

Pyrolytic conversion of sewage sludge into biochar could be a sustainable management option for Mediterranean agricultural soils. The aim of this work is to evaluate the effects of biochar from sewage sludge pyrolysis on soil properties; heavy metals solubility and bioavailability in a Mediterranean agricultural soil and compared with those of raw sewage sludge. Biochar (B) was prepared by pyrolysis of selected sewage sludge (SL) at 500°C. The pyrolysis process decreased the plant-available of Cu, Ni, Zn and Pb, the mobile forms of Cu, Ni, Zn, Cd and Pb and also the risk of leaching of Cu, Ni, Zn and Cd. A selected Mediterranean soil was amended with SL and B at two different rates in mass: 4% and 8%. The incubation experiment (200d) was conducted in order to study carbon mineralization and trace metal solubility and bioavailability of these treatments. Both types of amendments increased soil respiration with respect to the control soil. The increase was lower in the case of B than when SL was directly added. Metals mobility was studied in soil after the incubation and it can be established that the risk of leaching of Cu, Ni and Zn were lower in the soil treated with biochar that in sewage sludge treatment. Biochar amended samples also reduced plant availability of Ni, Zn, Cd and Pb when compared to sewage sludge amended samples.

Organic Acid Enhanced Soil Risk Element (Cd, Pb and Zn) Leaching and Secondary Bioconcentration in Water Lettuce (Pistia Stratiotes L.) in the Rhizofiltration Process

The use of natural chelates to enhance risk element mobility combined with rhizofiltration by free floating macrophytes have not been thoroughly studied in recent years. The aim of this study was to investigate the efficiency of organic acids in soil by conducting flushing experiments to enhance the mobility of Cd, Pb, and Zn from soil to solution. In addition, the bioaccumulation of Cd, Pb, and Zn, in water lettuce (Pistia stratiotes L.) will be studied as they affect the biomass in the rhizofiltration process. The results revealed that citric and tartaric acids mobilised the highest amount of all risk elements. In comparison to control, citric acid mobilised 71%, 181%, and 112% of Cd, Pb, and Zn while tartaric acid mobilised 70%, 155%, and 135% of Cd, Pb, and Zn respectively. The bioconcentration factor was approximately 2–5 times higher for juvenile plants than mature plants for all treatments as well as for both parts (leaves and roots). The risk element translocation into aerial parts decreased with increased time. Juvenile and mature plants proved a high accumulation potential and a 3 week growth period was observed as a sufficient time period to remove more than 80% of Cd, Pb, and Zn.

Effect of the addition of industrial by-products on Cu, Zn, Pb and As leachability in a mine sediment

A series of incubation and leaching experiments were performed to assess the feasibility of three industrial by-products (red gypsum (RG), sugar foam (SF) and ashes from the combustion of biomass (ACB)) to reduce the leachability of Cu, Pb, Zn and As in a sediment of São Domingos mine (Portugal). The changes in the element solid phase speciation were also evaluated by applying a sequential extraction procedure. All amendments significantly reduced the leachability of Zn and Cu, whereas the treatment with RG+SF+ACB also decreased the mobility of As. The reduction in Cu leachability was especially remarkable. This could be due to the great affinity of carbonates (included in SF and SF+ACB amendments) to precipitate with Cu, and maghemite and rutile (RG amendment) for acting as relevant sorbents for Cu. Pb was the least mobile element in the sediment and none of the treatments reduced its mobility. The sequential extraction reveals that the amendments induced a significant decrease in the concentration of elements associated with the residual fraction. Cu, Pb and As are redistributed from the residual fraction to the Al, Fe, and Mn hydr(oxides) fraction and Zn from the residual fraction to the water/acid soluble, exchangeable and bound to carbonates pool.

Experimental and numerical analysis of metal leaching from fly ash-amended highway bases

A study was conducted to evaluate the leaching potential of unpaved road materials (URM) mixed with lime activated high carbon fly ashes and to evaluate groundwater impacts of barium, boron, copper, and zinc leaching. This objective was met by a combination of batch water leach tests, column leach tests, and computer modeling. The laboratory tests were conducted on soil alone, fly ash alone, and URM–fly ash–lime kiln dust mixtures. The results indicated that an increase in fly ash and lime content has significant effects on leaching behavior of heavy metals from URM–fly ash mixture. An increase in fly ash content and a decrease in lime content promoted leaching of Ba, B and Cu whereas Zn leaching was primarily affected by the fly ash content. Numerically predicted field metal concentrations were significantly lower than the peak metal concentrations obtained in laboratory column leach tests, and field concentrations decreased with time and distance due to dispersion in soil vadose zone.

A facile route for preparing a mesoporous palladium coordination polymer as a recyclable heterogeneous catalyst

To overcome the separation difficulty of the palladium-based homogeneous catalyst, the palladium complex can be anchored on various supports such as silica, polymers and nanoparticles. For the same purpose, we describe a general and facile method to immobilize palladium bis(phosphine) complexes on the basis of the technique widely used for metal-organic framework (MOF) synthesis, yielding a mesoporous coordination polymer palladium-CP1. Although palladium complexes are generally not stable enough to allow further manipulation, we succeeded in preparation of a palladium coordination polymer without by-product Pd clusters or nanoparticles. The fresh palladium-CP1 catalyst exhibits a yield close to 55% for tolane at room temperature and 24 h in Sonogashira coupling of iodobenzene and phenylacetylene, as compared with a yield of 89% for its homogeneous counterpart [Pd(PPh(3))(2)Cl(2)]. Furthermore, this catalyst is stable enough to be reused more than four times with no Pd and Zn leaching. Therefore this new immobilization method offers great promise for the produce of recyclable palladium heterogeneous catalysts with higher activity and higher thermal and chemical stability in the future.

Effects of phosphorus amendments and plant growth on the mobility of Pb, Cu, and Zn in a multi-metal-contaminated soil

Phosphorus amendments have been widely and successfully used in immobilization of one single metal (e.g., Pb) in contaminated soils. However, application of P amendments in the immobilization of multiple metals and particularly investigations about the effects of planting on the stability of the initially P-induced immobilized metals in the contaminated soils are far limited. This study was conducted to determine the effects of phosphate rock tailing (PR), triple superphosphate fertilizer (TSP), and their combination (P+T) on mobility of Pb, Cu, and Zn in a multimetal-contaminated soil. Chinese cabbage (Brassica rapa subsp. chinensis) (metal-sensitive) and Chinese kale (Brassica alboglabra Bailey) (metal-resistant) were introduced to examine the effects of planting on leaching of Pb, Cu, and Zn in the P-amended soils. All three P treatments greatly reduced CaCl(2)-extractable Pb and Zn by 55.2-73.1% and 14.3-33.6%, respectively. The PR treatment decreased CaCl(2)-extractable Cu by 27.8%, while the TSP and P+T treatments increased it by 47.2% and 44.4%, respectively. All three P treatments were effective in reducing simulated rainwater leachable Pb, with dissolved and total leachable Pb decrease by 15.6-81.9% and 16.3-64.5%, respectively. The PR treatment reduced the total leachable Zn by 16.8%, while TSP and P+T treatments increased Zn leaching by 92.7% and 78.9%, respectively. However, total Cu leaching were elevated by 17.8-178% in all P treatments. Planting promoted the leaching of Pb and Cu by 98.7-127% and 23.5-170%, respectively, especially in the colloid fraction, whereas the leachable Zn was reduced by 95.3-96.5% due to planting. The P treatments reduced the uptake of Pb, Cu, and Zn in the aboveground parts of Chinese cabbage by up to 65.1%, 34.3%, and 9.59%, respectively. Though P treatments were effective in reducing Zn concentrations in the aboveground parts of the metal-resistant Chinese kale by 22.4-28.9%, they had little effect on Pb and Cu uptake. The results indicated that all P treatments were effective in immobilizing Pb. The effect on the immobilization of Cu and Zn varied with the different P treatments and evaluation methods. Metal-sensitive plants are more responsive to the P treatments than metal-resistant plants. Planting affects leaching of metals in the P-amended soils, specially leaching of colloid fraction. The conventional assessment on leaching risks of heavy metals by determining dissolved metals (filtered through 0.45-μm pore size membrane) in leachates could be underestimated since colloid fraction may also contribute to the leaching.

Antibacterial activity of heavy metal-loaded natural zeolite

The antibacterial activity of natural zeolitized tuffs containing 2.60 wt.% Cu 2+, 1.47 Zn 2+ or 0.52 Ni 2+ were tested. Antibacterial activities of the zeolites against Escherichia coli and Staphylococcus aureus were tested after 1 h and 24 h of exposure to 1 g of the zeolite in 100 mL of three different media, namely Luria Bertani, synthetic wastewater and secondary effluent wastewater. The antibacterial activities of the zeolites in Luria Bertani medium were significantly lower than those in the other media and negatively correlated with the chemical oxygen demand of the media. The Ni-loaded zeolite showed high leaching of Ni 2+ (3.44–9.13 wt.% of the Ni 2+ loaded) and weak antibacterial activity in the effluent water. Since Cu-loaded zeolite did not leach Cu 2+ and the leaching of Zn 2+ from Zn-loaded zeolite was low (1.07–1.61 wt.% of the Zn 2+ loaded), the strong antibacterial activity classified the Cu- and Zn-loaded zeolite as promising antibacterial materials for disinfection of secondary effluent water.

Research on Chloride Leaching of Cu, Zn and Ag from Flotation Tailings

Mineralogical examinations of Asheler copper mine flotation tailings have been carried out. Results show that the major metal sulphide minerals are pyrite and the main gangue constituents are quartz, chlorite-serpentine and muscovite. The main valuable metals are Cu, Zn and Ag. Basic mineral compositions of copper and zinc have been identified through chemical phase analysis. On the basis of mineralogical examinations, leaching test has been carried out in about 240g/l NaCl solution. The optimum conditions for leaching are found as follows: temperature at 86°C, pulp concentration is 24.19%wt, [Cu2+] =19.22g/l, [HCl] initial =0.17mol/L. Under these conditions, chloride leaching can extract 83.35%Cu, 92.10%Zn, and 85.26%Ag after 8 hours leaching.

Effect of weathering on the mobility of zinc in municipal solid waste incinerator bottom ash

This work describes the effect of weathering of fresh quenched municipal solid waste incinerator (MSWI) bottom ash on the mobility and leaching behavior of zinc (Zn). A sequential extraction procedure (SEP) was used to characterize the fractionation of zinc in the fresh and weathered MSWI bottom ash samples. It showed that the stable fraction of Zn, including organic matter bound fraction and residual fraction decreased from 62.4% to 30.9% during the weathering treatment, while the mobile fraction, including exchangeable fraction, carbonate bound fraction and Fe–Mn oxides bound fraction, increased from 37.6% to 60.1%. Furthermore, two standard leaching procedures, synthetic precipitation leaching procedure (SPLP) and toxicity characteristic leaching procedure (TCLP), were carried out on the fresh and weathered samples. The leaching of Zn was attenuated with the weathering treatment in the SPLP procedure, but enhanced in the TCLP procedure. The SEP and TCLP results suggested that the weathering treatment could enhance the mobility of Zn, which was distinct from previous work.

Heavy metal immobilization by cost-effective amendments in a contaminated soil: Effects on metal leaching and phytoavailability

The combination of revegetation and application of stabilizing soil amendments on heavy metal-contaminated soils is generally considered to be a promising alternative to expensive classical remediation techniques. Here, we simultaneously investigated the effects of six cost-effective amendments (CaCO3, iron grit, fly ash, manure, bentonite and bone meal) on Cd, Zn and Pb leaching and phytoavailability (assessed using white lupin, Lupinus albus L.). The Cd and Zn leaching was reduced by all amendments mainly due to alkalinity increase. The Pb leaching was strongly affected by the dissolved organic carbon (DOC) release. Therefore, bone meal and manure treatments, which highly increased DOC concentrations in leachates, increased the flow-weighted mean Pb concentrations by 2.3 and 16 times, respectively. Surprisingly, while iron grit induced strong Cd and Pb leaching reductions, this amendment doubled Cd and Pb concentrations in shoots of white lupin. Conversely, the addition of bone meal reduced Pb concentrations in shoots by 74%, probably because organo-Pb complexes (predicted using Visual MINTEQ) were largely dominant in solution. Overall, the addition of CaCO3 offered the best compromise as it successfully reduced both the leaching and the phytoavailability of the three considered metals. Our results demonstrate the efficacy of several amendments while stressing the need to measure simultaneously the leaching and the phytoavailability of metals induced by each amendment.

The Influence of Soil Properties on the Mobility of Metals Following a Single Application of Polluted Sewage Sludge to Seventy Agricultural Topsoils: A Laboratory Column Study

The main aim of this study was to examine the influence of soil properties on the leaching of Cd, Cr, Cu, Ni, Pb, and Zn following the application of polluted sewage sludge to contrasting topsoils. Seventy agricultural soil samples from different parts of Spain were amended with a single dose of sewage sludge (equivalent to 50 t dry weight ha−1) and a column study was performed under controlled conditions. After two, four, and six months of incubation, 283 ml of distilled water (equivalent to a rainfall event of 25 l m−2) was applied. The leachates were then collected and analyzed for metals. For all of the soils considered, the pH was the most important parameter for the control of mobility metals (except for Cu, determined by the sand and soil organic carbon and only to a lesser extent by the soil pH r2 = 0.604, p < 0.001) and was negatively related to all of the studied metals. For Pb and Zn, soil pH was the single soil property explaining their mobility (r2 = 0.411, p < 0.001 for Pb; r2 = 0.713, p < 0.001 for Zn) while for Cd, Cr and Ni, EC, sand and silt also appeared in the statistical models (r2 = 0.753, p < 0.001 for Cd; r2 = 0.366, p < 0.001 for Cr; r2 = 0.784, p < 0.001 for Ni). In the basic soils, soil texture was the most important soil property controlling the mobility of metals (except for that of Pb, which it only weakly predicted). For the acidic-neutral soils, the soil pH was the most important soil property controlling metal mobility (except for that of Cr, which was mainly determined by the pseudo-total Cr content).