Migration and enrichment of trace elements of Lower Palaeozoic carbonate rock strata in Beijing

Abstract

Analyses of trace elements of the Lower Palaeozoic carbonate rock strata in Beijing show that the contents of As, Hg, F increase from primary carbonate rocks to weathered carbonate rocks and from primary carbonate rocks to the soil coexisting with carbonate rocks, but the distribution regularity of S is not obvious. In the whole weathered stages, the sorption of As is mainly affected by Fe 2 O 3 . In soil Fe 2 O 3 is also the main affecting factor of Hg enrichment. The main existing forms of Hg in primary carbonate rocks should simply be physical adsorption, coprecipitation and false isomorphous form between surface of carbonate rock and Hg. In soil the enrichment of F has little relationship with sulfides and Fe 2 O 3 . In primary carbonate rocks, F is mainly absorbed by sulfides and clay minerals, etc. Weathered samples have closer genetic relationships with primary carbonate rocks. This also implies that weathered carbonate rocks have the close existing forms to that of primary carbonate rocks. In primary carbonate rocks FeS 2 and FeS are the main forms of S, and sulfides have fixation effect on some heavy metals, whereas in weathered carbonate rocks and soil the fixation effect is weakened. carbonate rocks, trace elements, Fe 2 O 3 , sulfide, clay mineral, enrichment As long geologic evolution processes and human activities accelerate the migration and enrichment of the harmful elements of primary carbonate rock, a series of ecologic problems emerged [1,2] . Numerous studies have been done about the heavy metal elements of the carbonate rock mines, waste rocks, residuals and soils [3][4][5][6][7][8][9] , but the systematic studies of trace elements have seldom done in primary carbonate rocks-weathered carbonate rocks-soil coexisting with carbonate rocks. This study focuses on the Lower Palaeozoic carbonate rocks in Beijing in order to uncover migration and enrichment of the trace elements such as As, Hg, S and F by comparing the contents of As, Hg, S, F in primary carbonates, weathered carbonate rocks and soil coexisting with carbonate rocks. Based on the different correlations between different elements combined with photomicrographic studies, migration and enrichment of the trace elements are discussed.

Enrichments of Cadmium and Arsenic and Their Effects on the Karst Forest Area

“…He et al [36] pointed out that the high concentration of Cd in the area was mainly distributed in exposed carbonate rocks. Ni et al [37] noted the enrichment trend of As in carbonate rocks of the Lower Paleozoic in Beijing by the symbiotic soil covering the rocks. In addition, the results of the 1:200,000 regional geochemical sweeping in Yunnan Province showed that the regions with geochemically high contents of As and Cd had good spatial coupling with widely distributed carbonates [14].…”