Date of Graduation

5-2017

Document Type

Thesis

Degree Name

Bachelor of Science in Chemical Engineering

Degree Level

Undergraduate

Department

Chemical Engineering

Advisor

Michael Ackerson

Reader

Roy Penney

Second Reader

Jamie Hestekin

Third Reader

Ed Clausen

Fourth Reader

David Ford

Abstract

Fugitive dust emissions from the storage and handling of mine tailings presents environmental and safety concerns, which must be addressed to promote the land sustainability and the health and safety of individuals around a tailings storage facility (TSF). The investigated dust control methods were agglomeration, binder slurry injection, and topical spray.

The Dust Busters determined that pelletizing was the most practical method of agglomeration. In order to produce durable pellets from the mine tailings, which consist primarily of silica, a binder must be added. A variety of binders were considered including magnesium and calcium chloride, bentonite, barite, cement, vinyl polymers, acrylic polymers, starch, carboxymethyl cellulose, and a commercial lignosulfonate/bitumen blend. Portland cement proved to be the most effective binder in regards to the pellet’s cost, structural integrity, and longevity. However, due to the abrasive nature of the tailings, pelletizing is not cost effective in comparison to other dust suppression techniques.

Binder slurry injection incorporates a pugmill mixer to inject a binding agent into the tailings slurry. Addition of a binder allows the slurry mixture to form a rigid crust that prevents fugitive dust once dried on the existing tailings dam. While the injected slurry is effective at minimizing dust emissions, it is not economically feasible due to high capital costs.

The most effective, environmentally safe, and economically feasible solution to reduce the dust associated with tailings storage facilities is a topical spray solution consisting of a vinyl copolymer. The vinyl copolymer, at relatively low concentrations, produces a robust yet permeable crust along the surface of the tailings, which is unmatched in comparison to the other binding agents. By applying the binder as topical solution rather than injecting the binder into the slurry, the capital cost for effective dust suppression is reduced by eliminating the additional process equipment required for both pelletizing and binder slurry injection. Treating 400 acres per year with a vinyl copolymer application costs $110,000. Existing equipment and personnel are adequate to change from the current magnesium chloride treatment to a vinyl copolymer treatment. Current yearly treatments using the magnesium chloride cost approximately $240,000-$720,000 assuming 1-3 applications per year across the 400 acre area; thus changing to a vinyl copolymer treatment will save $130,000-$390,000 per year.