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Structural and Raman spectroscopy studies of schultenite - phosphoschultenite isomorphic series

Młynarska M., Manecki M., Bajda T.

Geology, Geophysics and Environment

2014

Vol. 40, no. 1

110--111

In many countries, there is a problem of lead and arsenic soils contamination. Lead can be immobilized using phosphate amendments (Cao et al. 2003). This technique, however, results sometimes in arsenic migration. Mineral phases, which can precipitate in this conditions include schultenite PbHAsO4 and phosphoschultenite PbHPO4. Only recently it has been experimentally shown that these minerals can form a continuous solid solution series in Earth surface environments (Zembal 2012). Therefore, it is important to extend our knowledge on the properties of schultenitephos-phoschultenite solid solution series in order to solve certain environmental problems. For the first time, Raman spectroscopy was used to characterize schultenite, phosphoschultenite and their solid solutions. The main objective of this research is the identification and interpretation of systematic changes in the results of X-ray diffractometry and Raman spectroscopy applied to synthetic schultenites with various P to As ratio. Six samples were synthesized from aqueous solutions at ambient conditions. The ratio of P/(P + As) varied from 0 to 1 by 0.2 (Zembal 2012). Schultenite PbHAsO4 and phosphoschultenite PbHPO4 belong to monoclinic crystallographic system. The standard model of the P2/c symmetric group was used in the calculation of unit cell parameters. The results show systematic increase in unit cell parameters with substitution of P for As in the series: parameter a from 4,6737 to 4,8588, parameter b from 6,6381 to 6,7528 and parameter c from 5,7617 to 5,8495. The Raman spectra have also shown systematic variation in stretching and bending vibrations in the series. The ν1 stretching As-O band shifts from 463 cm-1 in schultenite PbHAsO4 to 469 cm-1 in P-substituted schultenite while ν 4 bending As-O band shifts form 824 cm-1 to 841 cm-1. Similar is observed in phosphoschultenite: the v1 stretching P-O band shifts from 555 cm-1 to 569 cm-1 and v bending P-O band shifts form 905 cm-1 to 940 cm-1 with increasing P content Observed shifts in position of Raman effects correlate linearly with As-P substitution: the bands originating from vibration modes shift to higher wave numbers with the substitution of P for As from schultenite PbHAsO4 towards phosphoschultenite PbHPO4. This can be explained by the fact that atomic mass of As is higher than that of P and that As-O bonds are longer than P-O bonds. The results extend our knowledge about schultenite-phosphoschultenite isomorphic series. Systematic shifts of Raman effects correlate strongly with chemical composition of analyzed phases. This is associated with systematic linear variation in the height (between 4,403 and 411 units for As-0 ν 4 bending band and between 825 and 70 units for P-0 v4 bending band) and area under certain peaks on Raman spectra (between 71,423 and 30,805 units for As-O ν 4 bending band and between 28,982 and 2,095 units for P-O ν 4 bending band). Current findings suggest that it is possible to estimate the overall P/(P+As) ratio in mineral samples by precise determination of the position and area under the respective Raman spectra and comparison with standard measurements.

Soil Contamination with Arsenic Versus the Content of Zinc in Plants

Najmowicz T., Wyszkowski M., Ciećko Z.

Ecological Chemistry and Engineering. A

2010

Vol. 17, nr 4-5

449-459

The aim of the study has been to reduce the effect of soil contamination with arsenic (10, 20, 30 and 40 mg As o kg-1) on the content of zinc in plants by the application of several substances (lime, natural! zeolite, charcoal, loam, compost and synthetic zeolite in experiments on maize; lime, natural zeolite, charcoal, loam, compost and synthetic zeolite in tests on cocksfoot and yellow lupine; peat, pine bark, dolomile and synthetic zeolite in trials on spring barley and swede). The soil improvers which were added in order to mollify the negative effect of arsenic on plants, in addition to the plant species and organs, were determined as a factor which modified the influence of soil contamination with arsenic on the content of zinc in plants. However, the effect of arsenic in soil on the amounts of zinc in yields of the test crops was ambiguous. Both positive and negative correlations occurred, albeit limited to individual cases, between the increasing quantities of arsenic in soil and the amounts of zinc in the yields of plants. Regarding the trials where no soil improvers had been applied, negative correlation was determined for the aboveground parts and roots of maize, aboveground parts of cocksfoot, roots of yellow lupine as well as grain and straw of barley. Positive correlation was discovered in the case of aboveground parts of Swedish turnip and roots of spring barley. The influence of some of the soil improvers on the content of zinc in the crops was sometimes greater than that of arsenic. Loam, lime, charcoal and compost produced the most evident and typically negative effect on the content of zinc in plant tissues. The influence of the other soil neutralizing substances on the content of zinc in plants depended on the plant species or organs.

Celem przeprowadzonych badań było zmniejszenie oddziaływania zanieczyszczenia gleby arsenem (10, 20, 30 i 40 mg As o kg-1) na zawartość cynku w roślinach przez stosowanie różnych substancji (wapno, zeolit naturalny, węgiel drzewny, ił, kompost w doświadczeniu z kukurydzą; wapno, zeolit naturalny, węgiel drzewny, ił, kompost i zeolit syntetyczny w badaniach z kupkówką i łubinem żółtym oraz torf, kora sosnowa, ił, dolomit i zeolit syntetyczny w doświadczeniach z jęczmieniem jarym i brukwią pastewną). Substancje zastosowane do złagodzenia wpływu arsenu na rośliny oraz ich gatunek i organ modyfikowały wpływ zanieczyszczenia gleby tym metalem na zawartość cynku w roślinach. Nie wykazano jednoznacznego oddziaływania zanieczyszczenia gleby arsenem na zawartość cynku w plonach badanych roślin. Odnotowano w pojedynczych przypadkach zarówno ujemne, jak i dodatnie korelacje pomiędzy rosnącym zanieczyszczeniem gleby arsenem a zawartością cynku w badanych organach roślin. W obiektach bez dodatków stwierdzono ujemną zależność dla zawartości cynku w częściach nadziemnych i korzeniach kukurydzy, częściach nadziemnych kupkówki, korzeniach łubinu żółtego oraz w ziarnie i słomie jęczmienia, a dodatnią w częściach nadziemnych brukwi pastewnej i korzeniach jęczmienia jarego. Wpływ niektórych dodatków neutralizujących na zawartość cynku był nawet większy niż arsenu. Najbardziej jednoznacznie i na ogół ujemnie na zawartość cynku w roślinach działały ił, wapno, węgiel drzewny i kompost. Wpływ pozostałych dodatków na zawartość cynku był często odmienny u różnych gatunków, a nawet organów testowanych roślin.