Waste minimization and treatment for ammonium bifluoride

Abstract

The Martin Marietta Ocala Plant processes copper plated wiring boards (PWB) for missile guided systems. The boards require several processing steps that use chemical baths. These chemical baths eventually become spent due to a build up of undesirable chemical species that contaminate the boards, and cause the boards to fail quality assurance tests. The spent baths are replaced, treated on site, and then disposed of off site. Martin Marietta contracted the University of Central Florida, Chemistry and Environmental Engineering Departments to develop treatment methodologies for the spent baths produced during PWB's processing. During phase I of the project, treatment methodologies were developed for all waste streams except for the ammonium bifluoride (ABF), NH4HF2, waste. Developing a treatment for the ABF waste was vital, as it represented 24% of the hazardous waste generated at the Ocala facility. A control guide for determining when the ABF bath was spent, and a treatment system for the spent ABF were developed during phase II of the project.

The ABF bath removes the glass burrs that are formed by the drilling of holes through stacks of PWB's. The ABF bath leaves a smooth, clean surface that can be electroless plated with copper. To avoid contamination of PWB's the ABF is replaced every two weeks regardless of the production rate. The problem of dumping on a calendar basis, is that production rates vary greatly and consequently "good" ABF baths are being dumped prior to expenditure. In addition, spent ABF can not be incorporated with the treatment processes for other waste streams containing fluoride, due to the high concentration of ammonium ion. The neutralization of the fluoride wastes would cause ammonia gas to evolve from the spent ABF, this is an undesirable byproduct. Attempts to remove the ammonium ion by oxidation with ozone, proved unsuccessful.

Dissolving of the glass burrs produces fluorosilicic acid (FSA), H2SiF6 As FSA increases in concentration, the effectiveness of the ABF decreases due to the loss of the reactive species, hydrofluoric acid. In addition, FSA participates in forming fluoride sludges that contaminate the PWB's. Therefore, the concentration of FSA was tracked during processing to determine if it can be used as a control guide to indicate when the ABF was spent.

The ABF manufacturer, recently suggested that copper can be used as a contol guide to determine when the ABF is spent. They recommended

dumping the ABF when it reached 700 ppm in copper. They found that copper forms a cupric chloride etch with hydrochloric acid, in the ABF, that causes "smutting" of the PWB's. Therefore, causing the PWB's to fail quality assurance tests. To remove these contaminates from the spent ABF, a treatment system using ion exchange resins was tested. The ion exchange resins were selected for their ability to remove copper and FSA at the pH of the spent ABF. To avoid contamination of the ion exchange resins, the ABF was filtered prior to being introduced to the resins. The effluent from the ion exchange columns was found to have a reduction in the copper and FSA concentrations. The reconditioned ABF can be recycled back into production. The resin columns were easily regenerated and can be reused to treat spent ABF. The waste eluted from the columns can be incorporated into present treatment processes at the Ocala facility. Review of the data, indicated that the monitoring of the copper concentration, can be used as a control for determining when the ABF bath is spent. The spent ABF can be recycled back into production, by using ion exchange resin that lowers the copper and FSA levels in the ABF bath.

Notes

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Graduation Date

1995

Semester

Fall

Advisor

Clausen, Christian

Degree

Master of Science (M.S.)

College

College of Arts and Sciences

Department

Chemistry

Degree Program

Industrial Chemistry

Format

PDF

Pages

49 p.

Language

English

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

Identifier

DP0028686

Subjects

Arts and Sciences -- Dissertations, Academic; Dissertations, Academic -- Arts and Sciences

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