Management of garnet waste generated from blasting metal structures

Garnet blasting is the current standard operation procedure for removal of deteriorated paint from metal structures at several oil- and gas-processing plants in the region, with thousands of tons of garnet being consumed annually for this purpose. Proper management of generated garnet waste is necessary to protect the environment, reduce cost, and save recourses. An approach based on the well-known hierarchy of waste management, with emphasis on waste recovery as the commonsense solution, was followed in this study. Two waste samples (one resulting from blasting onshore structures and the other from blasting offshore structures) were utilized. A thorough investigation to characterize the waste samples was conducted. Results revealed that garnet waste generated onshore does not pose any environmental concern but waste generated offshore is contaminated with oil and grease and has high zinc content. Results also showed that about 85% of the waste garnet falls in the range of the grain-size of new garnet. Physical and chemical characteristics of this fraction for the onshore garnet waste were similar to those of new garnet. The suitability of this fraction to be reused in garnet blasting was confirmed by a performance test. It was also demonstrated that the nonrecoverable waste fraction can be recycled in concrete construction without any impact on the strength of the concrete mix. Removal of oil and grease from the offshore garnet waste by combustion was explored. A minimum temperature of 500degreesC is needed to substantially decrease the level of oil and grease associated with the offshore garnet waste. Decontamination of the offshore garnet waste from zinc can be achieved by acid extraction to pass the TCLP test.