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SELECTIVE EXTRACTION AND PASSIVATION OF ARSENIC AND OTHER MICRO ELEMENTS OF ANTHROPOGENIC CONTAMINATED SOILS
Abstract
In the soil from the micro locality E-NE-SE around the OHIS factory, an increased degree of contamination with arsenic of anthropogenic origin has been detected. The objective of this research is an integral perception of the soil state with this pollutant, aiming to determine options for remediation of the contaminated soil. The basic parameters are being monitored for the extracted quantities of arsenic from various plant species that exist at the micro locality, in correlation with soil composition in the medium of the root system and the external factors. Intention is to define the affinity of the existing plants for available forms of arsenic. Two natural inorganic raw materials have been appointed as potential materials for remediation of contaminated soil with arsenic from the micro locality: diatomaceous earth from the locality of Slaviško Pole and trepel from the locality of Suvodol. Applying the extractors, their appropriate selective affinity and capacity for arsenic and other micro elements is evident.
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In the paper are shown results of the mineralogical-petrographical examinations of the trepel as a peculiar sedimentary rock of biogenetic origin from the Suvodol village near Bitola city, Republic of Macedonia. According to the microscopic (in polarizing translucent light), SEM, chemical, X-ray powder data was determined that examined trepel is composed mainly of opal (of biogenetic origin) as well as quartz, feldspars (plagioclases, K-feldspars), illite-hydromicas, chlorites of minor importance. Further examinations are in progress because the aforementioned results are based on one randomly selected trepel sample.
Arsenic, as the most common soil contaminant, was the subject of our research, presented in this publication. Namely, at the previous construction of the geochemical atlas of the presence of heavy toxic metals in the Skopje region soil, the area of about 300 km 2 has been explored. The analysis has been performed applying a semi quantitative method of ESA (Emission Spectral Analysis). The minimal detection limit for arsenic of this method is 100 ppm, so the obtained results did not show any value exceeding the previously pointed. Having in mind the probability of anthropogenic pollution of some segments of Skopje valley with arsenic, we enlarged our investigation as second phase of investigation applying the method of ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). According to this method the minimal detection limit for arsenic is 1 ppm, and four micro-localities of increased arsenic content were considered. In third phase has been a process of detailed grid analysis of arsenic contents in the top soil samples of specific micro-localties. With a statistical processing of data the following values of statistical parametres have been evaluated: number of samples (500), minimal detected content (< 0,3 ppm), maximal detected content (244,7 ppm), arithmetic mean (19 ppm), geometric mean ( 16 ppm), median ( 16 ppm), mean ( 16 ppm), standard deviation (1,8 ppm); threshold ( 20 ppm), threshold's double value (40 ppm); threshold's four times value (80 ppm); anomalous mean (> 80 ppm). The comparative frequency polygon, as well as the comparative diapason diagram were constructed.
According to the recent investigations, the terrains of the alluvial-Agricultural soils starting from the Ohis (organic chemical industry - Skopje), to East, North-east, South-east that is to the areas around the D. Lisice, G. Lisice, Dracevo and Ognjanci villages near Skopje, Macedonia, are treated as contaminated areas from As point of view. In the treated top soil samples from the mentioned region was discovered increased frequency of As contents in the range of 20-40 ppm as well as increased data for the arithmetic mean (about 25 ppm), geometric mean (19 ppm), and median (20 ppm).
The alluvial agricultural top soil samples of the Skopje field territory (of cca. 300 km2 - total surface) were investigated by the regional eco-geochemical mapping on the heavy-toxic metals: Pb, Zn, Cu, Ni, Cr, Ba, Y, As, determined by the emission spectral analyses. According to the achieved results were determined as follows: (1) contaminations of anthropogenic origin of Pb, Zn and Cu: Pb contents of increased amountsof cca. 70-100 ppm were determined in the soil samples around the main roads, railways, industrial complexes, etc.; Zn contents of increased amounts of cca. 150-200 ppm were determined in the soil samples around oil industry Okta, iron furnace industry, army square Goce Delcev, etc.; Cu contaminations of cca>30-70 ppm were determined in the top soil samples in the frame of 80-90% of the total investigate surface of the Skopje field territory; (2) contaminations of natural origin: in the investigated region of the Skopjefield territory in the agricultural top soil samples were determined Ni contaminations >601 ppm Ni; Cr contaminations (ranged from 400 >1000 ppm Cr) originated by the natural-weathering processes over the ultra-mafic (chromites-bearing) Radusha massif of thewider environments; Zr contaminations (with 80 > 100 ppm Zr contents) were determinedin the examined soil samples; Ba and Y contaminations are of minor importance.
With the complex examination of raw material from a new deposit in Slavishko Pole in the region of Kratovo–Zletovo volcanic area, Republic of Macedonia, its physical, chemical and mineralogical-petrographical properties have been defined. It has been found that it is a dominantly amorphous material, sedimen-tary rock of the type silicite-diatomite, with biogenic or phytogenic origin. The raw material consists of approximately 72% SiO 2 and it can be classified as diatomite of the type 1 (for 70–80% SiO 2) according to British Standard Specification (BS 1795:1976) [1]. Of the physical properties, more significant is porosity, which is higher than 60%. The raw material has a wide spectrum of possibilities for practical application: intensive absorbent for several types of liquids, regulator of physical and chemical properties of the soil, ionic substitution of heavy metals in soil, natural insecticide, clarifier in food industry etc. For determination of the chemical contents, properties and origin of the raw material the following methods have been used: silicate chemical analysis, XRD analysis, transmission optical mi-croscopy and other methods.
Arsenic is a semimetallic element that has been notorious for its toxicity and carcinogenicity. Arsenic exists in soils mainly as As (V) and As (III). Arsenate compounds predominate in aerobic soils and arsenite in slightly reduced soil. The objectives of this study were to investigate the effects of pH and the ability of the Pteris vittata on the absorption of arsenic anion. The removal of arsenic by Pteris vittata L. was observed at varying anion concentration and solubility As in an absorption plant. Preliminary results obtained with young plants on arsenic contaminated soil indicate that the arsenic was concentrated in the fronds and Pteris vittata L. absorption occur in alkaline environment.
Phytoremediation is an alternative technology to remove heavy metals in contaminated soil. Vetiveria zizanioides (Linn.) Nash (Surat Thani ecotype) and V. nemoralis (Balansa) A. Camus (Prachuabkirikhan ecotype) were chosen used for arsenic removal experiments. Both were studied plants after nursing forof one month. They were then were grown in the experimental potsof , which contained the soil with containing sodium arsenate ( Na 2 HAsO 4 .7H 2 O) at different concentrations (control, 50, 75, 100, 125, and 150 mgAs/kg soil). Three experiments were conducted for each concentration. Plants were harvested, and their growth observed for their growth and analyzed for the arsenic accumulation in theirits roots, stems and leaves after every 15 days up to 90 days. From the results, it was observed that all of the plants grew well in every concentration of arsenic, with 100% survival. In addition, V. zizanioides had number of plant per clump numbers and diameter of clump higher than V. nemoralis. In contrast, the height and dry weight of V. nemoralis was higher than of V. zizanioides. Accumulation of arsenic in the roots of both species was higher than in the leaf. The aAmount of arsenic accumulation in V. zizanioides was more than in V. nemoralis. In addition, arsenic removal efficiency of both species increased with increasing exposure time. The highest efficiency of V. zizanioides was very low, for the 90 day experimental duration of 90 days at a concentration of 75 mgAs/kg soil dry weight, and the highest efficiency of V. nemoralis was very low at 0.04 %, for the 90 day experimental duration of 90 days at a concentration of 125 mgAs/kg soil dry weight. Key word: vetiver, arsenic removal, phytoremediation
In situ chemical fixation represents a promising and potentially cost-effective treatment alternative for metal-contaminated soils. This article presents the findings of the use of iron-bearing soil amendments to reduce the leachability and bioaccessibility of arsenic in soils impacted by stack fallout from a zinc smelter. The focus of this investigation was to reduce the lead bioaccessibility of the soils through addition with phosphorus-bearing amendments. However, as phosphorus addition was expected to increase arsenic mobility, the fixation strategy also incorporated use of iron-bearing amendments to offset or reverse these effects. The findings of this investigation demonstrated that inclusion of iron-bearing chemicals in the amendment formulation reduced arsenic leachability and bioaccessibility without compromising amendment effectiveness for reducing lead bioaccessibility. These results suggest that in situ chemical fixation has the potential to be an effective strategy for treatment of the impacted soils. © 2003 Wiley Periodicals, Inc.
This greenhouse experiment evaluated arsenic removal by Pteris vittata and its effects on arsenic redistribution in soils. P. vittata grew in six arsenic-contaminated soils and its fronds were harvested and analyzed for arsenic in October, 2003, April, 2004, and October, 2004. The soil arsenic was separated into five fractions via sequential extraction. The ferns grew well and took up arsenic from all soils. Fern biomass ranged from 24.8 to 33.5 g plant(-1) after 4 months of growth but was reduced in the subsequent harvests. The frond arsenic concentrations ranged from 66 to 6,151 mg kg(-1), 110 to 3,056 mg kg(-1), and 162 to 2,139 mg kg(-1) from the first, second and third harvest, respectively. P. vittata reduced soil arsenic by 6.4-13% after three harvests. Arsenic in the soils was primarily associated with amorphous hydrous oxides (40-59%), which contributed the most to arsenic taken up by P. vittata (45-72%). It is possible to use P. vittata to remediate arsenic-contaminated soils by repeatedly harvesting its fronds.
- Vetiveria Nash
- Nemoralis
Nash and Vetiveria nemoralis (Balansa) A. Camus, Science Asia, 29, 291-296 (2003).