Sulfate leaching from recovered construction and demolition debris fines

摘要

Recovered soil fines are a product of the mechanical processing of construction and demolition (CD) debris for recycling. CD debris fines have been proposed as a substitute for soil in a number of applications. Questions have been raised regarding the potential environmental impact of sulfate leaching from particles of gypsum drywall in the soil fines. Sulfate has a secondary drinking water standard of 250 mg/1 and may convert to hydrogen sulfide during some reuse scenarios. Soil fines were collected from 13 CD debris recycling facilities in south Florida. A leaching study on the CD debris fines was performed to examine sulfate leachate concentrations resulting from both batch and column leaching experiments. The sulfate concentrations resulting from the batch leaching tests ranged from 890 to 1600 mg/1. The results of the column leaching tests also resulted in high sulfate concentrations. The source of sulfate in the debris fines was the dissolution of gypsum wallboard. The results from a multiple batch test indicated that the mass of the gypsum content in CD debris fines ranged from 1.5 to 9.1. The amount of gypsum that would be applied via soil fines during a typical resale scenario is greater than normal agricultural operations where gypsum is applied. When considering the beneficial reuse of CD debris fines, site-specific hydrogeology and appropriate state and local regulations for allowable sulfate concentrations in groundwater should be considered.