A Silica/Fly Ash-Based technology for Controlling Pyrite Oxidation. Page: 2 of 22
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
1. Overall Objective:
To develop methodologies by which sodium metasilicate or fly ash may produce an
effective coating on pyrite surfaces for inhibiting pyrite oxidation.
2. Broad Objective:
a. To evaluate the mechanisms by which a stable silica coating can be produced on the
surface of pyrite/pyritic coal waste using reagent grade sodium silicate.
b. To evaluate alternative oxidants (Na - hypochlorite or Ca - hypochlorite vs. hydrogen
peroxide) and pH buffers (acetate vs. bicarbonate) for the most cost effective silica coating
c. To evaluate the most effective method (based on results from "objective a and b") in
establishing silica coatings employing fly ash as silica source.
d. To evaluate durability of coating produced a) by sodium metasilicate, and b) by fly
ash; compare coating performance results with results obtained from control treatments and
traditional limestone treatments.
First six-month: Characterize pyrite surface reactions for understanding pyrite coating
establishment. Start a preliminary outdoor leaching - column experiment using 10 kg mine pyritic
spoil treated with silicates to evaluate potential application of coatings on a large scale.
Second six-month: Characterize silicate - iron reactions in solution and on pyrite surface for
understanding pyrite silica - coating formation.
Third six-month: Evaluate pyrite surface deposition of silicate having Na - silicate or fly
ash as source.
Fourth six-month: Evaluate silicate coating durability in large outdoor columns.
Pyrite in coal waste is initially oxidized by atmospheric 02, releasing acidity and Fe 2+ and
is the main source of acid mine drainage (AMD). At pH around 3, Fe2+ is rapidly oxidized by T.
ferrooxidans to Fe3+ which oxidize pyrite at a much faster rate than 02 (Singer and Strumm,
1970). Commonly, the approach used to control AMD in the field involves the use of limestone.
This approach, however, has a short span of effectiveness (Evangelou, 1995 and references
therein). The objective of a study carried out in our laboratory was to demonstrate that pyrite
oxidation could be controlled or inhibited through the formulation of an iron - oxide - silicate
coating on the surface of pyrite which would prevent either 02 or Fe3+ from further oxidizing
pyrite. Silica solubility is relatively constant for a wide pH range while relatively strong short-
range interactions between silicate ions and Fe3+ may make the latter (Fe3+) unavailable to
electron transfer processes (U. S. Gov., 1969). Ferric hydroxide-silica coating formation involved
leaching pyrite at room temperature with a solution containing H202,, NaOAc, and soluble
silicate at a flow rate of 0.43 ml min-I (Zang and Evangelou, 1998). It was postulated (based on
the results of our previous studies and on reported solubility behavior of silica in the presence of
Fe3+ (Iler, 1979)) that when H202 would reach the pyrite, its outermost layer would oxidize and
release Fe3+ which in the pH range of 4-6 would form an ferric hydroxide coating with some
form of polymerized silica. The ferric hydroxide-silica coating would be expected to significantly
Here’s what’s next.
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
A Silica/Fly Ash-Based technology for Controlling Pyrite Oxidation., report, September 21, 1997; United States. (digital.library.unt.edu/ark:/67531/metadc691633/m1/2/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.