Soil pollution by lead, zinc, cadmium and copper was characterized in the mine tailings and surrounding soils (arable and pasture lands) of an old Spanish Pb–Zn mine. Sixty soil samples were ...analyzed, determining the total metal concentration by acid digestion and the chemical fractionation of Pb and Zn by the modified BCR sequential extraction method. Samples belonging to mine waste areas showed the highest values, with mean concentrations of 28,453.50
mg
kg
−1 for Pb, 7000.44
mg
kg
−1 for Zn, 20.57
mg
kg
−1 for Cd and 308.48
mg
kg
−1 for Cu. High concentrations of Pb, Zn and Cd were found in many of the samples taken from surrounding arable and pasture lands, indicating a certain extent of spreading of heavy metal pollution. Acidic drainage and wind transport of dust were proposed as the main effects causing the dispersion of pollution. Sequential extraction showed that most of the Pb was associated with non-residual fractions, mainly in reducible form, in all the collected samples. Zn appeared mainly associated with the acid-extractable form in mine tailing samples, while the residual form was the predominant one in samples belonging to surrounding areas. Comparison of our results with several criteria reported in the literature for risk assessment in soils polluted by heavy metals showed the need to treat the mine tailings dumped in the mine area.
The effect of the earthworm
Lumbricus terrestris L. on metal availability in two mining soils was assessed by means of chemical extraction methods and a pot experiment using crop plants. Results from ...single and sequential extractions showed that
L. terrestris had a slight effect on metal fractionation in the studied soils: only metals bound to the soil organic matter were significantly increased in some cases. However, we found that
L. terrestris significantly increased root, shoot and total Pb and Zn concentrations in maize and barley for the soil with the highest concentrations of total and available metals. Specifically, shoot Pb concentration was increased by a factor of 7.5 and 3.9 for maize and barley, respectively, while shoot Zn concentration was increased by a factor of 3.7 and 1.7 for maize and barley, respectively. Our results demonstrated that earthworm activity increases the bioavailability of metals in soils.
►
Lumbricus terrestris L. activity increases the bioavailability of metals in soils. ► Earthworm activity can significantly increase total, shoot and root metal concentrations for crop plants. ► Both bioassays and chemical extraction methods are necessary for assessing the bioavailability of metals in contaminated soils.
Lumbricus terrestris L. activity increases the bioavailability of metals in soils and total, shoot and root metal concentrations for maize and barley.
► Effectiveness of thermal treatment in the immobilization of elements. ► Lightweight aggregates (LWAs) manufactured with contaminated mine soil and fly ash. ► Heat treatment was totally effective in ...the immobilization of most of the elements. ► The elements have become part of the LWA residual fraction. ► Heat treatment is detrimental from the standpoint of arsenic leaching.
This paper presents a study about the effectiveness of thermal treatment in the immobilization of different chemical elements within the structure of artificial lightweight aggregates (LWAs) manufactured with contaminated mine soil and fly ash. The heat treatment was totally effective in the immobilization of Cr, Ni, Cu, Zn, Pb, Be, Mn, Co and most of the rare earth elements. In the LWAs, they have become part of the residual fraction, probably forming the crystalline structure of neo-formed feldspars, of neo-formed minerals of the spinel group and the matrix. The thermal treatment was detrimental from the standpoint of arsenic leaching.
A sepiolite mining by-product (SEP) has been studied as major component for lightweight aggregate (LWA) manufacture. Pellet bursting during firing was avoided by the addition of 2.5 wt% of ...thermoplastic waste (P) and 2.5 wt% P + 2.5 wt% carbon fiber residue (FC) in powder form. The mixtures were pelletized and then sintered at 1225º˚C for 4 minutes in a rotary kiln. Highly porous white LWAs with good mechanical strength were produced. A mineralogical study revealed the formation of amorphous phase ( > 50%) and minor proportions of enstatite, protoenstatite and diopside. Quartz was the only inherited mineral, appearing in the form of isolated phenocrysts within a general porphyritic texture. The result of this study suggests the promising use of sepiolite (whether or not in residue form) for the manufacture of high quality LWAs.
Washing aggregate sludge from a gravel pit, fly ash of the Aliaga thermal power plant (Teruel, Spain) and used motor oil from cars have been physically, chemically and mineralogically characterized. ...They were mixed, milled and formed into pellets, pre-heated for 5
min and sintered in a rotary kiln at 1150
°C, 1175
°C, 1200
°C and 1225
°C for 10
min and 15
min at each temperature. The effect of raw material characteristics, heating temperatures and dwell times on loss on ignition (LOI), bloating index (BI), loose bulk density (
ρ
b), apparent and dry particle density (
ρ
a,
ρ
rd), voids (
H), water absorption (WA
24h) and compressive strength (
S) had been determined. All mixtures showed bloating potential taking into consideration the gases released at high temperatures, two of which were located inside and close to the “area of bloating”. The products obtained were lightweight aggregates (LWAs) in accordance with norm UNE-EN-13055-1 (
ρ
b
≤
1.20
g/cm
3 or particle density ≤2.00
g/cm
3). LWAs manufactured with 75%:25% and 50%:50% proportions of washing aggregate sludge:fly ash, heated at different temperatures and dwell times, were expanded LWAs (BI
>
0). They showed the lowest loose bulk density, the lowest dry and apparent particle density, the lowest water absorption and the highest compressive strength. It was possible to establish three groups of LWAs depending on their properties in comparison to
Arlita G3 and/or
F3, a commercially available lightweight aggregate manufactured in Spain. Our LWAs could have the same or similar applications of these commercial products, such as insulation, geotechnical applications, horticulture, gardening and/or prefabricated lightweight structures and insulation lightweight concretes.
The suitability of three new lightweight aggregates containing carbon fiber residues (CAs) as components in structural lightweight concrete has been studied. Prismatic concrete specimens were ...prepared using these CAs as a coarse fraction. Additional specimens of normal-weight aggregate, commercial lightweight aggregate and mortar were prepared for comparison. The CA-concrete samples (CACs) have yielded compressive strength values between 35 and 55 MPa as well as low density and thermal conductivity results. Furthermore, the CACs have displayed the highest ratios of mechanical strength over density and the thermal conductivity, which means that there is a better balance between their mechanical and physical properties than in the other samples studied. These results indicate that the new CAs could have great potential for use in structural lightweight concrete, also complying with the principles of the Circular Economy.
Washing aggregate sludge from a gravel pit, sewage sludge from a wastewater treatment plant (WWTP) and a clay-rich sediment have been physically, chemically and mineralogically characterized. They ...were mixed, milled and formed into pellets, pre-heated for 5
min and sintered in a rotary kiln at 1150
°C, 1175
°C, 1200
°C and 1225
°C for 10 and 15
min at each temperature. The effects of the raw material characteristics, heating temperatures and dwell times on the loss on ignition (LOI), bloating index (BI), bulk density (
ρ
b), apparent and dry particle densities (
ρ
a,
ρ
d), voids (
H), water absorption (WA
24h) and compressive strength (
S) were determined. All the mixtures presented a bloating potential taking into consideration the gases released at high temperatures. The products obtained were lightweight aggregates (LWAs) in accordance with Standard UNE-EN-13055-1 (
ρ
b
≤
1.20
g/cm
3 or particle density
≤
2.00
g/cm
3). LWAs manufactured with 50% washing aggregate sludge and 50% clay-rich sediment were expanded LWAs (BI
>
0) and showed the lowest apparent particle density, the lowest water absorption and the highest compressive strength. It was possible to establish three groups of LWAs on the basis of their properties in comparison to Arlita G3, F3 and F5, commercially available lightweight aggregates manufactured in Spain. Our LWAs may have the same or similar applications as these commercial products, such as horticulture, prefabricated lightweight structures and building structures.
The fractionation of five heavy metals in a washing aggregate sludge, a sewage sludge, a clay-rich sediment, the mixtures of these materials and the lightweight aggregates manufactured with them has ...been determined by applying the optimized European Community Bureau of Reference sequential extraction procedure in order to evaluate the effects of the heating process on the extraction of these elements. Additionally, preparation of eluates by aggregate leaching has been performed in accordance with the UNE-EN-H44-3 standard. The availability of all the studied heavy metals has been reduced by the thermal treatment, since most of the heavy metals have become part of the undigested material in the lightweight aggregates. Nickel has been the heavy metal that has presented the highest concentration in the eluates obtained after completion of the single extraction procedure in the lightweight aggregates. The studied lightweight aggregates may be used in lightweight concrete manufacturing from the standpoint of heavy metal leaching.
A pot experiment was conducted in order to assess the effect of the earthworm
Eisenia fetida on the uptake of Pb, Zn, Cd and Cu from soils polluted by mining activities using maize (
Zea mays) and ...barley (
Hordeum vulgare). Results from single and sequential extractions showed that the soil chemical partitioning of heavy metals was significantly changed by
E. fetida, leading to a higher concentration of metals in the non-residual fractions of the soil. Earthworm activities significantly increased shoot biomass (65% for maize and 73% for barley) and root metal concentration for all the metals under study in both maize and barley. The total accumulation rate values for Cd, Cu, Pb and Zn were significantly higher in the presence of
E. fetida for both crop plants. Those latter effects led to an increase in Zn extraction yields of up to 3.7-fold and 2.3-fold for barley and maize, respectively.
This paper presents the results of a study concerning the total and extractable concentrations of eight elements (As, Cd, Cr, Cu, Ni, Pb, Se and Zn) in soils and sediments from La Union mine (Toledo ...province, Castilla-La Mancha region, central Spain). It also presents the extent of the heavy metal contamination produced by the mining activities. Our results show that the study area can be considered as a heavily polluted site as consequence of the mining process carried out locally. This is demonstrated by the total concentrations of all studied elements, which are much higher than the World's and the Castilla-La Mancha's averages for soils. The elements that present the highest concentrations (total and extractable) are zinc and lead. Sediments show higher mean total concentrations than soils for all the studied elements. They also show the highest extractable concentrations due to the influence of the stream in the weathering of this type of materials. The areas affected by high concentrations of arsenic and heavy metals depend on the studied element, reaching the maximum extension and importance for lead and zinc. In the study area, the environmental damage can be increased by the low pH obtained since it implies an increase in the mobility of most of the studied elements.
•La Union mine (central Spain) can be considered as a heavily polluted site.•Elements that present the highest total and extractable concentrations are Zn and Pb.•The areas affected by high element concentrations depend on the studied heavy metal.•The environmental damage can be increased by low pH and high conductivity values.
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