Sediment features and heavy metal levels in four areas of Sardinia devoted to bivalve culture = Caratteristiche dei sedimenti e livelli di metalli pesanti in quattro aree della Sardegna idonee all’allevamento dei bivalvi

Sediment characteristics and Cd, Cu, Mn, Pb and Zn concentrations were assessed in the lagoons of Marceddì, Calich and Porto Pozzo, and in the inner part of the Gulf of Olbia. Sediment of the zones examined were quite similar, except for the Calich lagoon that showed the higher content of total organic carbon. High values of Cd, Pb and Zn were detected in the sediments of the Marceddì lagoon, while remarkable levels of Cu and Mn were found in the Calich lagoon and in the Gulf of Olbia

Studio dell'interazione dell'arseniato e del fosfato con i fanghi rossi, residui della lavorazione della bauxite, attraverso tecniche chimiche, spettroscopiche e termiche

The aim of this thesis was to study the interaction mechanisms between an inorganic sorbent, red mud (RM), and two different anions, arsenate and phosphate. Adsorption isotherms and sequential extraction procedures were firstly used to investigate these interactions. Sorption isotherms of arsenate and phosphate on RM, at pH 4.0, 7.0 and 10.0, were obtained while a sequential extraction procedure using H2O, (NH4)2SO4, NH4H2PO4, NH4 +-oxalate and NH4 +- oxalate + ascorbic acid, was applied to saturated RM samples to determine the interaction strength between respective anions and sorbent. Moreover, a physical, chemical and mineralogical characterization of not treated RM (alumina industry by-product) and RM exchanged with anions was carried out using spectroscopic techniques (FT–IR spectroscopy and X-Ray diffraction) and thermal analysis (TG and DTG) to evaluate the general suitability of RM as sorbent of phosphate and arsenate. Results showed that the RM was an effective sorbent of both arsenate and phosphate at all the pH values tested even if, as expected, the sorption capacity increased as the pH decreased. However, it was worth noting the different retention behaviors of the two anions on RM. Particularly, phosphate adsorption on RM at pH 4 was higher 2.6 times than arsenate adsorption. A different reactivity of the anions considered, likely due to different interaction of phosphate and arsenate with the mineralogical phases of RM, was also observed. In particular, the phosphate uptake capacity of RM was much greater than that shown for arsenate. X-ray diffraction pattern of RM exchanges with phosphate at pH 4 and 7, revealed additional phase, berlinite [AlPO4]. Overall, the results from this study suggest that RM could be a useful and environmentallyfriendly alternative for the “in-situ” and time-effective immobilization of arsenic in contaminated soils

Study of sorption processes and FT-IR analysis of arsenate sorbed onto red muds (a bauxite ore processing waste)

In this study we evaluated the arsenate adsorption capacity of red muds (RM), wastes tailing from the alumina production, at different pH values (4, 7, and 10). RM samples were artificially enriched in batch tests with solutions containing increasing concentrations of As(V). The pH of the solution significantly affected the adsorption, which increased with the decrease of pH. Moreover a sequential extraction procedure [H2O; (NH4)2SO4; NH4H2PO4; NH4+-oxalate; NH4+-oxalate + ascorbic acid] was applied to RM samples exchanged with arsenate. Using this approach it was shown that low concentrations of arsenate sorbed in RM were present as water soluble and exchangeable fractions, while NH4+-oxalate and NH4+-oxalate + ascorbic acid extracted most of the adsorbed arsenate from RM at different pH values. Besides, FT-IR spectroscopy was used to better understand the nature of RM surface configuration after As(V) sorption. In the FT-IR spectra the presence of As(V) species was highlighted by a well resolved band at 865 cm−1. The intensity and broadness of this band increased at the decreasing of pH. This band could be related to ν(As–O) vibration of an inner-sphere Al–O–As complex and/or due to As–O bonds of the adsorbed As(V) species on Fe oxides of RM samples

Influence of the pH on the accumulation of phosphate by red mud (a bauxite ore processing waste)

In the present work we investigated the interactions established between red mud (RM) and phosphate anions (P) at pH 4.0, 7.0 and 10.0. The amount of P sorbed by RM (P-RM) increased as the pH decreased being equal to 4.871 mmol g−1 at pH 4.0, 0.924 mmol g−1 at pH 7.0, and 0.266 mmol g−1 at pH 10.0. Sequential extractions’ data of P-RM equilibrated at pH 4.0 and 7.0, suggested that the phosphate sorption at these pH values was mainly regulated by two different mechanisms that gave rise to a chemical adsorption on RM phases, and to the formation of metal phosphate precipitates. By contrast, at pH 10.0 the P-sorption was regulated by a chemisorption mechanism on Fe–Al phases of RM. These findings were supported by FT-IR analysis, which showed a broad band at 1114 and 1105 cm−1 in P-RM spectra at pH 4.0 and 7.0 respectively, attributable to P–O(H) stretching ν3-modes associated to inner-sphere complexes of phosphate on Fe–Al phases, or alternatively to stretching vibrations of PO43− tetrahedra, arising from a precipitate of aluminium phosphate. Importantly, the FT-IR spectroscopy showed a phosphate-promoted dissolution of tectosilicates, notably cancrinite and sodalite, in RM exchanged with phosphate at pH 4.0 and 7.0

X-ray diffraction and thermal analysis of bauxite ore-processing waste (red mud) exchanged with arsenate and phosphate

The use of waste materials from mineral ore processing has much potential for immobilizing pollutants such as arsenic (As) in natural soils and waters. The purpose of the present study was to investigate red mud (RM, a finely textured bauxite-ore residue) as a sequestering agent for arsenate and phosphate, including characterization of the types of surface complexes formed. The mineralogical and structural changes occurring in RM were investigated after exchange with arsenate [As(V)-RM] and phosphate [P(V)-RM] anions at pH 4.0, 7.0, and 10.0. Eight different phases were present in the untreated red mud (RMnt), though 80 wt.% of the crystalline phase consisted of sodalite, hematite, gibbsite, and boehmite. The X-ray diffraction (XRD) data for As(V)-RM revealed an anion-promoted dissolution of the gibbsite, suggesting that this phase was the most active for As(V) sequestration. In addition, the lattice parameters of cancrinite were different in As(V)-RM at pH 7.0 and 10.0 from those in RMnt. The changes may be related to the incorporation of arsenate in the cancrinite cages. X-ray diffraction patterns of P(V)-RM at pH 4.0 and 7.0 revealed the dissolution of sodalite, hematite, and gibbsite, and the formation of a novel phase, berlinite [(α,β)AlPO4]. The new phases detected through XRD and thermal (TG/DTG) analysis in P(V)-RM probably originated through an initial phosphate-promoted dissolution of some RM phases, followed by a precipitation reaction between the phosphate and Al/Fe ions. The results obtained suggest that phosphate and arsenate, though with different reactivities, were strongly bound to some RM phases, such as gibbsite, cancrinite, sodalite, and hematite through mechanisms such as chemical sorption and coprecipitation reactions. The knowledge acquired will be helpful in selecting alternative materials such as red muds, which currently pose critical economic and environmental challenges related to their disposal, for the decontamination of soils and waters polluted with As

XRD, FTIR, and thermal analysis of bauxite ore-processing waste (red mud) exchanged with heavy metals

The present work shows the results of X-ray diffraction (XRD), Fourier transform infrared (FTIR), and thermal analysis of untreated (RM) and acid-treated red mud (RM), a bauxite ore-processing waste, exchanged with Pb, Cd, and Zn cations. These studies were performed in order to investigate the changes in the sorbent structure caused by the exchange with metals of different ionic radii. The XRD pattern of RM, analyzed according to the Rietveld method, showed a mixture of eight different phases. However, just three phases made up 78 wt.% of the RM: cancrinite (33 wt.%), hematite (29 wt.%), and sodalite (16 wt.%). X-ray diffraction patterns of RM exchanged with Pb and Cd cations revealed two additional phases, namely hydrocerussite [Pb(CO) (OH) (10 wt.%)] and octavite [CdCO (8 wt.%)]. These two phases probably originated from the carbonate precipitation processes which were due to the decarbonation of cancrinite. Hydrocerussite and octavite were not found in the case of acid-treated red mud samples. In the FTIR spectra, the introduction of cations caused a distinct shift to higher wavenumbers in the peak at ∼1100 cm, which is attributed to the asymmetric stretch of Si-O-Al. This effect may be associated with the Pb, Cd, and Zn adsorbed by the red muds which caused a deformation of the initial structure. Thermal analysis data of the red mud samples were obtained by thermogravimetric/differential thermogravimetric analysis, and these methods were employed to evaluate the desorption behavior of water and to clarify the thermal stability of the chemical phases of the different red mud samples. The loss of metal-bound water in the red mud samples was found to depend on the size of non-framework cations and water loss consistently followed the order: Zn>Cd>Pb

Copper(II) andlead(II)removal from aqueous solution by water treatment residues

In this study, we investigated the ability of Fe- and Al-based water treatment residues (Fe- and Al-WTR) to accumulate Pb(II) and Cu(II) at pH 4.5. The role of the inorganic and organic fractions of WTRs in metals sorption was also assessed. Sorption isotherms showed a higher sorption of Pb(II) by both WTRs with respect to Cu(II) (e.g. 0.105 and 0.089 mmol g−1 of Pb(II) and Cu(II) respectively sorbed by Fe-WTR). Fe-WTR revealed a stronger sorbent for both metals than Al-WTR. The amount of Pb(II) and Cu(II) sorbed by Fe-WTR was about the 69% and 63% higher than that sorbed by the Al-WTR. The organic matter of Fe- and Al-WTR contributed to about 26% and 8.5% respectively in the sorption of both metals. The sequential extraction procedure showed that the greatest amount of metals sorbed by both WTRs were tightly bound and not extractable, and this was particularly apparent for Cu(II). The FT-IR spectra indicated the formation of inner-sphere complexes between the Fe(Al)–O nucleus and Pb(II) and Cu(II). Moreover, the FT-IR spectra also suggested that the humic fraction of WTRs interacted, through the carboxylate groups, with Cu(II) and Pb(II) by forming mainly monodentate and bidentate complexes, respectively

Long-term influence of red mud on As mobility and soil physico-chemical and microbial parameters in a polluted sub-acidic soil

In this study we evaluated the efficiency of red muds (RM, a bauxite residue) to immobilize the arsenic present in a polluted sub-acidic soil (UP-soil; total As 2428 mg kg−1) and to influence some chemical, biochemical and microbiological properties after 2 years since RM addition. The RM addition caused a pH increase, a striking decrease of total organic carbon and a significant increase of water-soluble C, N and P. The analysis of As mobility through sequential extraction showed a reduction of the water-soluble arsenic in the RM-soil compared to the UP-soil (3.44% and 5.59% of the total As respectively) and a remarkable increase of the residual (non extractable) arsenic fraction in the RM-soil (>300% compared to UP-soil). RM addition increased significantly the microbial abundance and the activity of selected enzymes (dehydrogenase, urease) with respect to UP-soil while had a major influence on the structure of soil microbial communities as evaluated by the Biolog Community Level Physiological Profile. The reduced As mobility, together with an increase of C, N and P labile-pool (likely originating from a “de-structuring effect” of RM on the soil organic matter) were identified as the key factors affecting the biological activity in the RM-treated soil

Interaction of the water soluble fraction of MSW-composts with Pb(II) and Cu(II) ions

In this study we report on the interactions between the water-soluble fraction (WSF) of two municipal solid waste composts (C1- and C2-WSF) with Pb(II) and Cu(II) ions at pH 4.5. The Me(II) addition to the compost-WSFs led to the formation of soluble Me(II)-organic complexes (as highlighted by FT-IR spectroscopy), and to a decrease of the trace metals' solubility, which was greater for Pb(II) than Cu(II). This was due to the formation of insoluble Me(II) complexes involving the water-soluble organic carbon (WSOC) and the inorganic anions within both WSFs [1.10 and 0.62 mmol L−1 and 2.06 and 0.42 mmol L−1 of Pb(II) and Cu(II) precipitated from C1- and C2-WSF respectively, when 6.4 mmol L−1 Me(II) was added]. A loss of WSOC from both WSFs, i.e. ∼13% and <5%, was detected in the systems containing 6.4 mmol L−1 Pb(II) and Cu(II) respectively. A significant contribution in the formation of Pb(II) precipitates was also due to phosphate, chloride and sulphate anions, since their concentrations in the WSF decreased of 80, 25 and 90%, respectively, after the addition of 6.4 mmol L−1 Pb(II). A decrease of phosphate anions in both WSFs (∼30%) was found in the systems containing Cu(II)