Benjamin Greene

Selective recovery of gold and other metal ions from an algal biomass.

The authors observed that the pH dependence of the binding of Au/sup 3 +/, Ag/sup +/, and Hg/sup 2 +/ to the algae Chlorella vulgaris is different than the binding of other metal ions. Between pH 5 and 7, a variety of metal ions bind strongly to the cell surface. Most of these algal-bound metal ions can be selectively desorbed by lowering the pH to 2; however, Au/sup 3 +/, Hg/sup 2 +/, and Ag/sup +/ are all bound strongly at pH 2. Addition of a strong ligand at different pHs is required to elute these ions from the algal surface. Algal-bound gold and mercury can be selectively eluted by using mercaptoethanol. An elution scheme is demonstrated for the binding and selective recovery of Cu/sup 2 +/, Zn/sup 2 +/, Au/sup 3 +/, and Hg/sup 2 +/ from an equimolar mixture. 20 references, 2 figures.

Accumulation of elemental gold on the alga Chlorella vulgaris

Abstract The accumulation of Au(0) by lyophilized preparations of the alga Chlorella vulgaris has been investigated. Gold is bound to the algae upon suspending dried algal cells in solutions containing hydrogen tetrachloroaurate (III). Relative amounts of ionic and atomic algal-bound gold were determined by thiourea extraction. It was found that the amount of algal-bound atomic gold produced from ionic gold increased with time. The effect of algal-bound gold concentration on the rate and extent of gold reduction was observed. It is suggested that at least three different classes of sites are available for gold binding and reduction. The effect of Au(0) accumulation on the binding ability of gold-bound algae was also investigated, and an apparent enhancement of gold binding ability is reported.

Carbon paste electrodes modified with cation-exchange resin in differential pulse voltammetry

Abstract Chemically modified carbon paste eletrodes are prepared by incorporating appropriate quantities of a cation-exchange resin directly into the paste mixture. Ionic analytes can be preconcentrated on these electrodes by an ion-exchange reaction rather than electrolytic plating. Differential pulse voltammetry is used to quantify the accumulated ions. The response is characterized with respect to preconcentration period, bulk concentration, pH, paste composition, reproducibility, and other variables. Copper ion is used as a test system. The procedure exhibits good linearity for 6.25 × 10−5−3.0 × 10−4 M copper(II) ions and the peak current varies linearly with preconcentration time between 1 and 7 min for the conditions used.

Anodic stripping voltammetry of heavy metals with a flow injection system

The design and operation of an anodic stripping voltammetric system based on the flow injection technique are described. A flow cell with a wall-jet glassy carbon disk electrode and a 500-μl sample volume are employed. The system allows trace metals at the μg l-1 level to be quantified simultaneusly at a rate of ten samples per hour. A low differential pulse background current allows a detection limit for lead of about 3 × 10-9 M (0.3 ng) with a 3-min deposition time. Deposition is done in the presence of oxygen in the sample solution, but the carrier solution is oxygen-free.

Direct Determination of Gold in Solid Algal Cells by Direct Current Argon Plasma Emission Spectrometry with Introduction by Electrothermal Atomization

Abstract A direct, rapid, and sensitive method for determining gold in dried solid algal cells using an electrothermal atomization - direct

Reliability of background current subtraction in anodic stripping voltammetry at mercury film electrodes

Abstract The effectiveness and accuracy of the correction for background current in subtractive anodic stripping voltammetry at rotating mercury film electrodes are discussed. The effects of different experimental parameters on the subtracted baseline are examined. Long deposition periods, at extreme potentials, result in large errors in the background correction. The incomplete background correction is attributed mainly to changes in the morphology of the working electrode. Different approaches for obtaining the subtractive stripping response are compared. Errors are reduced when subtractive differential pulse stripping is used at different convection rates, resulting in a detection limit of 2 × 10-9 M cadmium with 1-min deposition. Cadmium, lead, and zinc ions at nano molar concentrations were used as test ions.

Observations on the Determination of Uranium in Waters by Direct Current Argon Plasma Emission Spectrometry

Abstract This paper reports observations on the determination of uranium in ground and mine waters by direct current argon plasma emission spectrometry. An enhancement effect due to different concentrations of six sodium salts and calcium nitrate was characterized. When the salt concentration of the waters was greater than the aqueous uranium standards, an erroneous uranium signal was found. The method of standard additions showed that direct calibration with aqueous uranium standards containing 0.05M sodium acetate was satisfactory. The use of matrix matched uranium standards is recommended to compensate for large enhancements in the uranium emission signal that may result from the presence of naturally occurring salts. Concentrations of uranium in ground waters ranged from 5 ppm to 16 ppm depending on sampling site and in mine waters from 2 ppm to several hundred ppm.

Direct Determination of Mercury in Solid Algal Cells by Direct-Current Argon-Plasma Emission Spectrometry with Sample Introduction by Electrothermal Vaporization

A study on the use of electrothermal vaporization for introduction of solid samples into a direct-current plasma is presented. The solid samples investigated were milligram masses of an alga exposed to various mercury solutions. The results are independent of the algal mass in the 0.6–9 mg range, and give acceptable calibration curves up to 20 mg of mercury absorbed on 5-mg masses of the alga; the relative standard deviation was 7.4% for nine successive samples of 100μg of mercury absorbed by a mass of approximately 3 mg of algal cells. Various mercury compounds gave more than one peak, with different appearance times. Addition of sulphur-containing algal cells or cysteine modified the mercury signal, making it the same (for the compounds tested) irrespective of the mercury compound originally present.