Carleton R. Bern

UNEXPECTED DOMINANCE OF PARENT-MATERIAL STRONTIUM IN A TROPICAL FOREST ON HIGHLY WEATHERED SOILS

Controls over nutrient supply are key to understanding the structure and functioning of terrestrial ecosystems. Conceptual models once held that in situ mineral weathering was the primary long-term control over the availability of many plant nutrients, including the base cations calcium (Ca), magnesium (Mg), and potassium (K). Recent evidence has shown that atmospheric sources of these “rock-derived” nutrients can dominate actively cycling ecosystem pools, especially in systems on highly weathered soils. Such studies have relied heavily on the use of strontium isotopes as a proxy for base-cation cycling. Here we show that vegetation and soil-exchangeable pools of strontium in a tropical rainforest on highly weathered soils are still dominated by local rock sources. This pattern exists despite substantial atmospheric inputs of Sr, Ca, K, and Mg, and despite nearly 100% depletion of these elements from the top 1 m of soil. We present a model demonstrating that modest weathering inputs, resulting from tectonically driven erosion, could maintain parent-material dominance of actively cycling Sr. The majority of tropical forests are on highly weathered soils, but our results suggest that these forests may still show considerable variation in their primary sources of essential nutrients.

The role of water in unconventional in situ energy resource extraction technologies: Chapter 7 in Food, energy, and water: The chemistry connection

Global trends toward developing new energy resources from lower grade, larger tonnage deposits that are not generally accessible using “conventional” extraction methods involve variations of subsurface in situ extraction techniques including in situ oil shale retorting, hydraulic fracturing of petroleum reservoirs, and in situ recovery of uranium. Although these methods are economically feasible and perhaps result in a smaller above-ground land-use footprint, there remain uncertainties regarding potential subsurface impacts to groundwater. This chapter provides an overview of the role of water in these technologies and the opportunities and challenges for water reuse and recycling.

REE Distribution and Mobility in Regolith Formed on Granite Bedrock of the Southeast United States

Rare earth elements (REE) ion-adsorption clay deposits are of global economic importance. There is considerable ambiguity regarding the origin and global distribution of the deposit type, which is currently mined only in South China. While all weathered materials may contain some exchangeable REE, the importance of weathering of REEenriched parent material is in the generation of high concentrations of selected REE. Ionadsorption clay deposits of China have grades from ~500 to over 3000 ppm total rare earth oxide. South China clay deposits enriched in heavy REE relative to light REE currently supply virtually all of the heavy REE to global markets (Yang et al., 2013). We present results of mineralogical, REE geochemistry and radiogenic isotope (Nd-Sr-Pb) studies of weathered metaluminous-to-alkaline igneous rocks of the Southeast United States. Our studies are aimed at understanding the genesis of REE-enriched regolith profiles and how that information can be used to discern whether there is significant potential for economic REE ion-adsorption clay deposits in the United States. The main criteria of this deposit model include the presence of large igneous suites, generally granitic rocks; long periods of intense weathering with little subsequent erosion; and evidence for mobility and enrichment of REE within the developing regolith profile. Source rocks for the South China deposits are described mainly as granitic rocks that range from calc-alkaline to alkaline compositions. REE mobilization processes are thought to include late-magmatic-to-deuteric alteration and deep lateritic weathering. The REEs can occur as ionic REE adsorbed to clay, and as secondary REE-carbonate and/or phosphate minerals. 2 Weathered Granites from the Southeast United States

Laboratory data from testing parameters of EPA Method 3060A on Soils Contaminated with Chromium or Processing Residue

It has been shown that EPA Method 3060A does not adequately extract Cr(VI) from solids containing chromium ore processing residue (COPR). We systematically tested modifications to prescribed parameters of EPA 3060A towards improving extraction efficiency of Cr(VI) from NIST SRM 2701, a standard COPR-contaminated soil from New Jersey (NJ). The alkaline extraction fluid leached Al, Si, and B from the prescribed borosilicate glass vessels which interfered with Cr(VI) extraction from COPR. The use of polytetrafluoroethylene (PTFE) vessels increased the extraction efficiency. Intensive grinding of NIST 2701 resulted in the extraction of 730±30 mg kg-1 Cr(VI), which is substantially greater than the certified Cr(VI) value of 551±35 mg kg-1 but still less than the Cr(VI) value of ~3000 mg kg-1 previously determined by X-ray absorption near edge structure (XANES) spectroscopy. Increasing the extraction fluid to sample ratio also increased the efficiency of Cr(VI) extraction. Ratios similar to the 20 mL g-1 prescribed by 3060A resulted in low and highly variable extraction efficiencies. Ratios of 900 mL g-1 or greater resulted in relatively consistent extraction, yielding as much as ~950 mg kg-1 Cr(VI) from intensively ground NIST 2701 after 2.25 hours of extraction. Increasing the extraction time to 48 hours resulted in up to 1274 mg kg-1.

Modifications to EPA Method 3060A to Improve Extraction of Cr(VI) from Chromium Ore Processing Residue-Contaminated Soils

It has been shown that EPA Method 3060A does not adequately extract Cr(VI) from chromium ore processing residue (COPR). We modified various parameters of EPA 3060A toward understanding the transformation of COPR minerals in the alkaline extraction and improving extraction of Cr(VI) from NIST SRM 2701, a standard COPR-contaminated soil. Aluminum and Si were the major elements dissolved from NIST 2701, and their concentrations in solution were correlated with Cr(VI). The extraction fluid leached additional Al and Si from the method-prescribed borosilicate glass vessels which appeared to suppress the release of Cr(VI). Use of polytetrafluoroethylene vessels and intensive grinding of NIST 2701 increased the amount of Cr(VI) extracted. These modifications, combined with an increased extraction fluid to sample ratio of ≥900 mL g-1 and 48-h extraction time resulted in a maximum release of 1274 ± 7 mg kg-1 Cr(VI). This is greater than the NIST 2701 certified value of 551 ± 35 mg kg-1 but less than 3050 mg kg-1 Cr(VI) previously estimated by X-ray absorption near edge structure spectroscopy. Some of the increased Cr(VI) may have resulted from oxidation of Cr(III) released from brownmillerite which rapidly transformed during the extractions. Layered-double hydroxides remained stable during extractions and represent a potential residence for unextracted Cr(VI).