In Massachusetts, sulfuric acid is considered integral to many processes making the search for alternatives challenging. In some applications however, alternatives for reducing byproduct or eliminating use are both cost and technically effective.
Sulfuric acid is often used to control pH and to regenerate ion exchange resins. Alternatives processes or creating new vendor relationships have reduced or eliminated the use of sulfuric acid in many companies.
- Carbon dioxide is an alternative to sulfuric acid when used for pH control. As demonstrated in the Toxics Use Reduction Institute's Demonstration Sites Program, Massachusetts' Cranston Print Works eliminated 1.9 million pounds of sulfuric acid by substituting a liquid carbon dioxide process to neutralize wastewater. A case study by the Office of Technical Assistance documents a 99% reduction of sulfuric acid at Standard Uniform Services in Agawam by installing a similar system.
- Reverse osmosis can be used instead of ion exchange so that acid is not needed to regenerate the ion exchange resins. Traditionally ion exchange has been more popular than reverse osmosis due to a lower capital cost and 100% use of the treated water (compared to 70%-90% with reverse osmosis). However, the capital costs of reverse osmosis systems are becoming more competitive and they do not require the use and associated cost of any regeneration chemical. In 1994 The Robbins Company of Attleboro reduced its acid use by nearly 100% by replacing an ion exchange system with a reverse osmosis system for water treatment.
- Refuse Energy System Company in Saugus won a Governor's Award for Outstanding Achievement in Toxics Use Reduction partly for reducing its sulfuric acid use by 67%. The company first determined the true water quality needs for its boiler operations. The company then negotiated a service performance contract with its supplier to pay a flat fee for a certain level of water conditioning. The chemical supplier then has motivation to minimize chemical use.
Sulfuric acid is commonly used for cleaning. Previously regulations may have been a barrier to companies to reduce use or switch to alternatives.
- When used to clean food processing tanks, its use may be specifically required by regulations of the U.S. Food and Drug Administration (FDA). However, a search of the Toxics Use Reduction Institute's database of cleaning chemistries found 10 non-sulfuric acid-containing chemistries that have FDA approval. These products may be substitutes, depending on the application.
- The semiconductor industry uses ultra-pure, concentrated sulfuric acid to clean silicon wafers. Recycling or reusing the spent acid is inhibited by perceived RCRA (Resource Conservation and Recovery Act) barriers identified through the U.S. EPA's Common Sense Initiative. The EPA is currently preparing an information sheet to encourage recycling of this acid.
In electronics and surface finishing operations, sulfuric acid is used in many processes including etching, pickling and anodizing.
- In electronics manufacture, two sulfuric-acid containing micro-etch solutions are used: sulfuric acid/hydrogen peroxide, and persulfate (typically peroxydisulfate). The sulfuric/peroxide systems use considerably more sulfuric acid than the persulfate systems, but the bath life of the sulfuric/peroxide systems can be increased by continuously removing the copper using an electrolytic plate-out cell and reusing the etch solution.
- In the electroplating pickling process, sulfuric acid can be replaced by hydrochloric acid or phosphoric acid, each with their own associated hazards. Diffusion dialysis can extend the bath life of an acid pickling solution with substantial savings in sulfuric acid purchases and waste volumes. For copper and tin plating, the pickling baths do not degrade readily and the major losses can be reduced by reducing dragout.
Dragout is a continual source of loss and must be minimized. This can be accomplished by removing the workpiece at a slower rate, increasing drip time, installing drain boards or drip bars between baths, maintaining racking designs for maximum draining, and installing air knives or spray or fog rinses above process tanks.
Sulfuric acid losses from anodizing operations are partially a function of dragout, but also of aluminum build-up in the bath. Both diffusion dialysis and acid sorption can extend the lives of these baths and are generally cost effective, even for smaller operations.
- Anodizers also use sulfuric acid combined with hydrofluoric acid and nitric acid to remove smut from cast aluminum. The triacid combination is necessary due to silicon addition prior to casting, which must be removed by the presence of the fluoride ion. Non-cast aluminum can be desmutted using either a 1:1 concentrated nitric acid to water solution or with a low concentration nitric acid solution (~4% HNO3 with an iron salt). If an anodizer is processing both cast and non-cast aluminum, and if the facility has available space, two desmutting processes can be used to lessen the load on the sulfuric acid-containing bath.
- In addition, the less acid that must be treated by the waste treatment process in these operations, the less neutralization chemical will be required.
US Environmental Protection Agency, 1992, "Guides to Pollution Prevention The Metal Finishing Industry" (Washington, D.C.); Toxics Use Reduction Institute, Printed Wiring Board Industry Module, TUR Planner's Certification Course, Rev 2.1, (Lowell Massachusetts, TURI), Toxics Use Reduction Institute 1996, Technical Report No. 31 "Toxics Use Reduction Through Process Improvement, Substitution & Integral Recycling" (Lowell Massachusetts, TURI); EPA website http://www.epa.gov/ooaujeag/csi/computer/accomp12.htm; Office of Technical Assistance, Toxics Use Reduction Case Study, "Elimination of TURA Chemical Reporting at The Robbins Company," (Boston, Massachusetts, see webpage:http://www.state.ma.us/ota/cases/robbins.htm); Office of Technical Assistance, Toxics Use Reduction Case Study, "Sulfuric Acid Reduction at Standard Uniform Services," (Boston, Massachusetts, see webpage: http://www.state.ma.us/ota/cases/standard.htm).