Precipitation and coprecipitation in the presence of chelating agents. IV. Precipitation of barium chromate from EDTA

Abstract At many mining sites process (milling) and drainage waters escape treatment and cause receiving waters to become contaminated above avoidance or even toxic levels for fish. The present know-how on chemical agents which can be used to complex with copper and zinc to form non-toxic compounds is limited to chelating agents such as NTA or EDTA. Preferential reaction with trivalent ions such as iron means that such ions must be tied up before complexation of copper and zinc can occur. As the amount of iron in contaminated water is usually two to eight times higher than that of copper and zinc, high dosages of chelating agents are usually required. In this project, the use of salts of anthranilic acid, especially calcium anthranilate, was investigated. The consumption of anthranilateions was found to be about the same as that of NTA or EDTA, i.e. four milligrams per milligram of copper or zinc. The total dosage to be applied to contaminated waters would be, however, several times lower as iron is not involved in the reactions and copper and zinc are complexed in that order. Toxicity tests to compare the efficiency and dasages of calcium anthranilate and NTA or EDTA are presently being carried out.

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DO WEAK OR STRONG ACIDS REMOVE CARBONATE CONTAMINATION FROM ANCIENT TOOTH ENAMEL MORE EFFECTIVELY? THE EFFECT OF ACID PRETREATMENT ON RADIOCARBON AND δ13C ANALYSES

Radiocarbon ◽

10.1017/rdc.2021.32 ◽

2021 ◽

pp. 1-18

Author(s):

Rachel Wood ◽

Andre Barros Curado Fleury ◽

Stewart Fallon ◽

Thi Mai Huong Nguyen ◽

Anh Tuan Nguyen

Keyword(s):

Acetic Acid ◽

Chelating Agents ◽

Tooth Enamel ◽

Mineral Phase ◽

Acid Pretreatment ◽

Skeletal Material ◽

Lower Porosity ◽

Hot Environments ◽

Strong Acids

ABSTRACT In hot environments, collagen, which is normally targeted when radiocarbon (14C) dating bone, rapidly degrades. With little other skeletal material suitable for 14C dating, it can be impossible to obtain dates directly on skeletal materials. A small amount of carbonate occurs in hydroxyapatite, the mineral phase of bone and tooth enamel, and has been used as an alternative to collagen. Unfortunately, the mineral phase is often heavily contaminated with exogenous carbonate causing 14C dates to underestimate the true age of a sample. Although tooth enamel, with its larger, more stable crystals and lower porosity, is likely to be more robust to diagenesis than bone, little work has been undertaken to investigate how exogenous carbonate can be effectively removed prior to 14C dating. Typically, acid is used to dissolve calcite and etch the surface of the enamel, but it is unclear which acid is most effective. This study repeats and extends earlier work using a wider range of samples and acids and chelating agents (hydrochloric, lactic, acetic and propionic acids, and EDTA). We find that weaker acids remove carbonate contaminants more effectively than stronger acids, and acetic acid is the most effective. However, accurate dates cannot always be obtained.

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