Date of Award

1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology

First Advisor

D. Perkins, III

Abstract

Many compounds, including Thio-Red® and 2,4,6-trimercaptotriazine, trisodium salt (TMT-55), have been marketed to precipitate mercury and other heavy metals from water, including contaminated ground waters. For the products to be effective, information is needed on the chemistry of the products, how they precipitate metals from aqueous solutions, and the chemistries and stabilities of the precipitates.

CS32-, HS-, and S2- are the dominant sulfur species in Thio-Red®. They precipitate heavy metals from water as sulfides (e.g., HgS, PbS, and ZnS). Thio-Red® also contains traces of poisonous carbon disulfide (CS2). Additional CS2 could form from reactions between dissolved heavy metals and CS32-. Large volumes of undiluted Thio-Red® should not be injected into low oxygen environments for in situ restoration until studies eliminate the possibility of contamination from CS2 or H2S.

TMT-55 is Na3C3N3S3•9H20. The crystallographic data at 25°C are R3, Z = 6, a= 17.600(1) A, c = 9.720(2) A, V= 2607.5(5) A3, and a density of 1.55 g/cm3•

The precipitation of divalent mercury with TMT-55 may produce one or more mercury 2,4,6-trimercaptotriazine (HgTMT) compounds, including white, greenish yellow to greenish brown, gray, or yellow varieties. The white variety probably contains mercury(I). White HgTMT is monoclinic with a= 5.904(3) A, b = 6.966(1) A, c = 4.572(1) A, /3= 104.85(2)0, and V= 181.79 A3. Within three months, white HgTMT may decompose in air or aerated water to the yellow or gray varieties. In batch leachates with distilled and deionized water, white HgTMT may release more than 3 milligrams/liter of mercury. Mercury concentrations in water leachates of gray and bright yellow samples are relatively low (3.3 - 53 micrograms/liter). The gray, yellow and greenish varieties still require extensive chemical analyses and leaching studies to identify any leachable organic compounds. TMT-55 should not be used in the in situ restoration of mercury contaminated sites until the resulting precipitates are known to be stable.

Studies ofBalC3N3S3) 2•8H20 and BaHiC3N3S3) 2•4.5H20 (BaTMT compounds) were initiated to determine ifTMT-55 could be used to remove barium from water. However, the aqueous solubilities of both compounds are probably too high (around 5 grams/liter) for effective barium removal.

The results of powder XRD analyses show that B(C3N3S3) 2•8H20 is either hexagonal or orthorhombic. The results of a single crystal analysis of BaHiC3N3S3) 2•4.5H20 at 25°C state that the compound is monoclinic (P2/c) with Z = 4, calculated density= 2.077 g/cm3, a= 8.5576(4) A, b = 21.028(1) A, c = 20.276(1) A, /J= 96.440(1)0, and V= 3625.6(3) A3.

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