Esperanza Álvarez-Rodríguez

Pine bark as bio-adsorbent for Cd, Cu, Ni, Pb and Zn: Batch-type and stirred flow chamber experiments

The objective of this work was to determine the retention of five metals on pine bark using stirred flow and batch-type experiments. Resulting from batch-type kinetic experiments, adsorption was rapid, with no significant differences for the various contact times. Adsorption was between 98 and 99% for Pb(2+), 83-84% for Cu(2+), 78-84% for Cd(2+), 77-83% for Zn(2+), and 70-75% for Ni(2+), and it was faster for low concentrations, with Pb suffering the highest retention, followed by Cu, Cd, Ni and Zn. The fitting to the Freundlich and Langmuir models was satisfactory. Desorption increased in parallel to the added concentrations, with Pb always showing the lowest levels. Stirred flow chamber experiments showed strong hysteresis for Pb and Cu, sorption being mostly irreversible. The differences affecting the studied heavy metals are mainly due to different affinity for the adsorption sites. Pine bark can be used to effectively remove Pb and Cu from polluted environments.

Kinetics of Hg(II) adsorption and desorption in calcined mussel shells

The potential use of calcined mussel shells to purify water contaminated with mercury was evaluated. The Hg(II) adsorption and desorption kinetics were studied in batch-type and stirred-flow chamber experiments. The adsorption/desorption experiments revealed some differences between the batches of shells used. The batch of shells that displayed the greatest capacity to adsorb Hg(II), via a highly irreversible reaction, also contained more Fe and Al than the other batches. The results of the stirred-flow chamber experiments indicated a high degree of irreversibility in the process of Hg(II) adsorption in the mussel shell, and that Hg(II) was rapidly retained. The results of these experiments also revealed that the efficiency of depuration differed depending on the length of time that the system was used: when the system was operated for 55 min, depurating 162 mL of inflowing water g(-1) mussel shell, a 90% reduction in the initial concentration of Hg(II) was obtained; use of the system for 90 min, depurating 265 mL water g(-1) mussel shell, produced a 75% reduction in the initial Hg(II), and use of the system for 162.5 min, depurating 487 mL of water g(-1) mussel shell, resulted in a 50% reduction in the initial Hg(II).

Heavy metal retention in copper mine soil treated with mussel shells: batch and column experiments.

Batch and column experiments are used to study the effects of ground mussel shell amendment on the retention of heavy metals in acidic mine soil. The soil pH increases proportionally with the mussel shell concentration employed. Mussel shell amendment increases Cu, Cd, Ni and Zn retention in mine soil when compared with unamended soil. In fact, Cu retention was 6480μmolkg(-1) (43% of the total added) when the maximum metal concentration (1570μM) was added to the unamended soil, whereas retention reached 15,039μmolkg(-1) (99.9% of the total Cu added) when soil was amended with 24gkg(-1) mussel shell; in the case of Cd, adsorption increases from 3257μmolkg(-1) (15% of the total added) for the unamended soil, to 13,200μmolkg(-1) (87% of the total added) for the shell-amended soil; Ni retention increased from 3767μmolkg(-1) (25% of the total added) corresponding to unamended soil, to 11,854μmolkg(-1) (77% of the total added) for the shell-amended soil; and finally, Zn retention increased from 4684μmolkg(-1) (31% of the total added), for unamended soil, to 14,952μmolkg(-1) (98% of the total added) for shell-amended soil. The results of the constant flow transport experiments show that the addition of the 24gkg(-1) mussel shells can retain Cu, Cd, Ni and Zn within the first few centimetres of the column length, indicating the usefulness of ground mussel shells to drastically decrease the mobility and availability of these pollutants and to facilitate soil remediation.

Study of metal transport through pine bark for reutilization as a biosorbent.

The potential utilization of pine bark as a biosorbent for the treatment of metal-contaminated soils and waters has been evaluated in transport experiments using laboratory columns. Solutions containing the metals Cu, Pb, Zn, Ni or Cd, each one individually and at three different concentrations (2.5, 10 and 25 mM) were tested. Pine bark affected metal transport and the breakthrough curves, producing a reduction of their concentrations in the solution and a clear retardation with respect to an inert tracer. At metal concentrations equal to 2.5 mM, 100% of the assayed elements were removed from the solution in the pine bark column. At the 10 mM metal concentration, the percentage of metals retained fell to 38-67% of the amount added, whereas at the 25 mM metal concentration, only 16-43% was retained. In all cases, the highest retention capacity corresponded to Pb, and the lowest to Zn, whereas Cu, Cd and Ni produced intermediate comparable results. The analysis of the pine bark within the columns after the transport experiment showed that the metals entering the column adsorb progressively until a saturation concentration is reached in the whole column, and only then they can be released at significant concentrations. This saturation concentration was approximately 70 mmol kg(-1) for Cd, Ni and Zn, 100 mmol kg(-1) for Cu, and 125 mmol kg(-1) for Pb. Overall, our experiments have shown the high effectiveness of pine bark to retain the assayed metals in stable forms of low mobility.

Competitive adsorption/desorption of tetracycline, oxytetracycline and chlortetracycline on two acid soils: Stirred flow chamber experiments

The objective of this work was to study the competitive adsorption/desorption of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) on two acid soils. We used the stirred flow chamber technique to obtain experimental data on rapid kinetic processes affecting the retention/release of the antibiotics. Both adsorption and desorption were higher on soil 1 (which showed the highest carbon, clay and Al and Fe oxides content) than on soil 2. Moreover, hysteresis affected the adsorption/desorption processes. Experimental data were fitted to a pseudo-first order equation, resulting qamax (adsorption maximum) values that were higher for soil 1 than for soil 2, and indicating that CTC competed with TC more intensely than OTC in soil 1. Regarding soil 2, the values corresponding to the adsorption kinetics constants (ka) and desorption kinetics constants for fast sites (kd1), followed a trend inverse to qamax and qdmax respectively. In conclusion, competition affected adsorption/desorption kinetics for the three antibiotics assayed, and thus retention/release and subsequent transport processes in soil and water environments.

Competitive adsorption and transport of Cd, Cu, Ni and Zn in a mine soil amended with mussel shell

Batch type and column experiments were used to study competitive adsorption-desorption and transport for Cd, Cu, Ni and Zn in a mine soil, both un-amended and amended with mussel shell. Batch type experiments showed that adsorption was affected by the added concentration of the metals, generally following the sequence Cu>Zn>Cd≈Ni. Metal desorbed was a function of the dose of metal added, as well as of the dose of shell amendment, being relevant that even when the highest dose of metal (2300 μM) was added, the 24 g kg(-1) shell amendment caused a drastic diminution in the amount of metal desorbed. Column experiments showed that even the lowest dose of the shell amendment (6 g kg(-1)) caused a strong retention of the 4 heavy metals assayed, whereas using the 24 g kg(-1) shell amendment no metal was detected in the effluent during the time of the experiment. The mass of metal retained in the un-amended soil was very different for the various metals assayed, but the amendment with 6 g kg(-1) shell increased this retention in all cases, and the 24 g kg(-1) amendment caused almost 100% retention for all 4 metals. The retardation factor (R) suffered an overall increase as a function of the shell dose; the profile distribution of the 4 heavy metals was homogeneous through the un-amended soil into the column, but the shell amendment clearly decreased the solute transport affecting these metals, causing its concentration in the first centimeters of the soil profile.

Mercury removal using ground and calcined mussel shell.

We determined mercury retention on calcined and ground mussel shell, in presence and absence of phosphate, using batch and stirred flow chamber experiments. In batch experiments the calcined shell exhibited higher Hg adsorption, with good fitting to Freundlich equation (R2: 0.925-0.978); the presence of phosphate increased Hg adsorption; mercury desorption was 13% or lower, diminishing up to 2% under the presence of phosphates. In stirred flow chamber experiments calcined shell retained more Hg than ground shells (6300 vs. 4000-5200 micromol/kg); Hg retention increased an additional 40% on calcined shell and up to an additional 70% on ground shells when phosphates were present; mercury desorption was quite similar in all shell types (20%-34%), increasing up to 49%-60% in ground shells when phosphates were present. The higher Hg adsorption on calcined shell would be related to its calcite and dolomite concentrations; mercury-phosphate interactions would cause the increase in Hg retention when phosphates are present. Data on Hg desorption suggest that Hg retention was not easily reversible after batch experiments, increasing in the stirred flow chamber due to convective flow. Calcined and ground mussel shells could be recycled removing Hg from water, with the presence of phosphates in solution improving efficacy.

As(V) and P Competitive Sorption on Soils, By-Products and Waste Materials.

Batch-type experiments were used to study competitive As(V) and P sorption on various soils and sorbent materials. The materials assayed were a forest soil, a vineyard soil, pyritic material, granitic material, coarsely and finely ground mussel shell, calcinated mussel shell ash, pine sawdust and slate processing fines. Competition between As(V) and P was pronounced in the case of both soils, granitic material, slate fines, both shells and pine sawdust, showing more affinity for P. Contrary, the pyritic material and mussel shell ash showed high and similar affinity for As(V) and P. These results could be useful to make a correct use of the soils and materials assayed when focusing on As and P removal in solid or liquid media, in circumstances where both pollutants may compete for sorption sites.

Lithological and land-use based assessment of heavy metal pollution in soils surrounding a cement plant in SW Europe.

We study the influence of phasing out a cement plant on the heavy metal (Hg, Pb and Cr) content in the surrounding soils, taking into account factors often neglected, such as contributions due to local lithology or land use. The range of total Hg was 10-144µg kg(-1), reaching up to 41 and 145mgkg(-1) for total contents of Pb and Cr, respectively. Forest soils showed higher concentration of Hg than prairie soils, indicating the importance of land use on the accumulation of volatile heavy metals in soils. In forest soils, total Hg showed a trend to decrease with soil depth, whereas in prairie soils the vertical pattern of heavy metal concentrations was quite homogeneous. In most cases, the distance to the cement plant was not a factor of influence in the soils content of the analyzed heavy metals. Total Pb and Cr contents in soils nearby the cement plant were quite similar to those found in the local lithology, resulting in enrichment factor values (EFs) below 2. This suggests that soil parent material is the main source of these heavy metals in the studied soils, while the contribution of the cement plant to Pb and Cr soil pollution was almost negligible. On the contrary, the soils surrounding the cement plant accumulate a significant amount of Hg, compared to the underlying lithology. This was especially noticeable in forest soils, where Hg EF achieved values up to 36. These results are of relevance, bearing in mind that Hg accumulation in soils may be an issue of environmental concern, particularly in prairie soils, where temporal flooding can favor Hg transformation to highly toxic methyl-Hg. In addition, the concurrence of acid soils and total-Cr concentrations in the range of those considered phytotoxic should be also stressed.

Valorization of biosorbent obtained from a forestry waste: Competitive adsorption, desorption and transport of Cd, Cu, Ni, Pb and Zn

Bark from Pinus pinaster is one of the most abundant forestry wastes in Europe, and among the proposed technologies for its reutilization, the removal of heavy metals from wastewater has been gaining increasing attention. In this work, we have studied the performance of pine bark for heavy metal biosorption on competitive systems. Pb, Cu, Ni, Zn and Cd sorption and desorption at equilibrium were studied in batch experiments, whereas transport was studied in column experiments. Batch experiments were performed adding simultaneously different concentrations (0.08-3.15mM) of two or more metals in solution to pine bark samples. Column experiments were performed with 10mM solutions of two metals or a 5mM solution of the five metals. In general, the results under competitive conditions were different to those obtained in monoelemental experiments. The multi-metal batch experiments showed the adsorption sequence Pb≈Cu>Cd>Zn>Ni for lower metal doses, Pb>Cu>Cd>Zn>Ni for intermediate doses, and Pb>Cu>Cd≈Zn≈Ni for high metal doses. Desorption followed the sequence Pb<Cd<Cu<Zn<Ni for the lowest metal doses, and Pb<Cu<Zn<Cd<Ni for the highest ones. The bi-metal batch experiments indicated that Cu and Pb suffered the highest retention, with high capacity to displace Cd, Ni and Zn from adsorption sites on pine bark. The transport experiments produced comparable results to those obtained in the batch experiments, with pine bark retention capacity following the sequence Pb>Cu>Zn>Cd>Ni. The presence of a second metal affected the transport of all the elements studied except Pb, and confirmed the strong influence of Pb and Cu on the retention of the other metals. These results can help to appropriately design decontamination systems using this forestry waste.