This invention relates to a process for manufacturing aggregate from the fly ash and bottom ash residues resulting from incineration of municipal solid waste.
Municipal solid waste consists essentially of household waste and non-hazardous commercial and industrial solid waste of the type which is typically collected from churches, schools, offices, restaurants, stores and light industrial facilities by the waste collection organization serving a particular municipality or other similar community. Most of the cast-offs of daily living in a complex modern society are found in typical municipal solid waste. Thus, municipal solid waste typically includes garbage, paper, textiles, plastics, glass, ceramics, metals, rubber, rock, earth, wood and other combustible and noncombustible materials in a variety of forms.
Final disposal of municipal solid waste has become a major problem in many urban areas of the United States and other developed countries. While various methods have been proposed, land disposal and incineration are the two methods which are most commonly used for final disposal of municipal solid waste. With the most commonly used method of land disposal, municipal solid waste is transported to and deposited in a sanitary landfill. Municipal solid waste often is pulverized or otherwise compacted to decrease its volume prior to land disposal.
Whether or not municipal solid waste is pulverized or otherwise compacted, sufficient vacant land with a hydrogeologic structure which is suitable for use as a landfill is often not available in many urban areas of the United States and other developed countries. Accordingly, it is desirable to have a method for final disposal of municipal solid waste which does not require deposit of significant quantities of waste in a landfill. Incineration reduces the municipal solid waste volume by up to ninety percent. However, the residue remaining must still be deposited in a landfill. If the fly ash and bottom ash residues resulting from incineration can be used to manufacture useful by-products, the landfill requirement would be substantially reduced.
Mass burn incineration is the most commonly used method for incineration of municipal solid waste. With mass burn incineration, non-hazardous, processable solid waste collected by the waste collection organization serving the particular municipality or other similar community is fed into an incinerator. With a less commonly used method, non-hazardous solid waste is processed in remove ferrous and non-ferrous metals, recycleable materials and identifiable non-combustible materials and then fed into an incinerator as refuse derived fuel. Steam for heating or electric power production is often a useful by-product of incineration. However, even when identifiable non-combustible material has been separated from combustible material prior to incineration, incineration of typical municipal solid waste generates significant quantities of fly ash and bottom ash residues containing ferrous and nonferrous metals. Such ash residues are typically deposited in a landfill.
The fly ash and bottom ash residues from incineration of typical municipal solid waste have two characteristics which often prevent their direct and immediate use as by-products. First, since non-combustible metals are present in typical municipal solid waste, such ash residues typically contain leachable heavy metals, such as lead and cadmium, which could constitute a potential hazard to the environment, including surface water supplies and aquifiers, if they are present in sufficient quantities and not managed properly. Second, each of such ash residues typically is volumetrically unstable for several months. Volumetric expansion will cause structural damage if either of such ash residues is used as a construction material during the period of instability.
A method of immobilizing leachable heavy metals in the fly ash residue resulting from incineration of municipal solid waste with lime and an inorganic sulfide is disclosed in U.S. Pat. No. 4,629,509. With that method, dry lime and an aqueous solution of a soluble inorganic sulfide are mixed with the fly ash residue following its discharge from a precipitator. While leachable heavy metals would appear to be effectively immobilized by that method, U.S. Pat. No. 4,629,509 does not disclose stabilization of the fly, bottom or combined ash residue to prevent volumetric expansion. Furthermore, no method or process for manufacturing any useful by-product from the fly, bottom or combined ash residue is disclosed by U.S. Pat. No. 4,629,509.