Reuse heavy metal wastes

Alternative hazardous waste management practices for the treatment of heavy metal wastes are necessary in order to comply with the current landfill ban requirements. In Washington State the priorities for managing hazardous waste are 1) reducing the volume or toxicity at the generation source 2) recycling recovery and reuse practices 3) treatment alternatives and 4) landfill. 

When antifreeze becomes unsuitable for use, either because of depletion of inhibitors, presence of corrosion products or corrosive ions, or degradation of the fluid, recycling and reuse of the antifreeze, rather than disposal, may be considered. Although ethylene glycol is readily biodegraded in typical municipal waste treatment faciHties, antifreeze disposal becomes problematic because the coolant may contain hazardous quantities of heavy metals picked up from the cooling system. Recycling may be economically preferred over coolant disposal and reduces the concern for environmental impact. 

The process can handle a wide range of materials, including heavy metal contaminated wastes. It is very fast compared to conventional processes and produces an easily handled product that can be used in construction. Waste CO2 can be captured and converted into carbonate to yield carbon credits. Target applications include pre-treatment of waste prior to disposal, recychng and reuse of industrial waste, and remediation of contaminated brownfield sites. 

Apatite, a natural calcium fluoride phosphate, can adsorb low to moderate levels of dissolved metals from soils, groundwater, and waste streams. Metals naturally chemically bind to the apatite, forming extremely stable phosphate phases of metal-substituted apatite minerals. This natural process is used by UFA Ventures, Inc., and is called phosphate-induced metals stabilization (PIMS). The PIMS material can by used in a packed bed, mixed with the contaminated media, or used as a permeable barrier. The material may be left in place, disposed of, or reused. It requires no further treatment or stabilization. Research is currently being conducted on using apatite to remediate soil and groundwater contaminated with heavy metals, and the technology may also be applicable to radionuclides. The technology is not yet commercially available. 

Reverse osmosis also serves some of the waste management and resource recovery needs in the metals and metal finishing industry. Effluent streams from mining and plating operations containing heavy metals, acids, and other chemicals can be treated with reverse osmosis to recover both the metal as its salt, and purified water for reuse. For metal ion recovery from dilute solutions, however, reverse osmosis faces competition from conventional solvent extraction, membrane-based solvent extraction, and its variant, coupled transport (see Section V.F.3). 

To clean a metal diffusion pump, it must be removed from the rest of the system. Pour the used oil (or mercury) into a proper receptacle. Do not throw the mercury away because it is a toxic waste (a heavy metal). Fortunately, mercury may be reclaimed and reused. As far as diffusion pump oils, check with the health and safety and/or environmental officer in your institution and/or the waste disposal management of your city. Be sure to mention any hazardous materials that may have been absorbed by the pump oil during its operation to the proper authorities. 

Spent Catalyst. Opportunities may exist to reduce the volume of waste catalyst by reusing the catalyst through several hydrogeneration batches however, experts disagree on the final benefit of this. The measurement of this can be made by measuring hydrogeneration efficiency versus catalyst disposal costs. Other catalysts have been explored however, their costs and effectiveness are less desirable. These catalysts have environmental problems of their own because they are heavy metal-based. 

Heavy Metals Heavy metals are usually added to wastewater from municipal commercial and industrial activities and may have to be removed if the waste-water is to be reused, or discharged into a water body. 

Electrolysis is the reaction of either oxidation or reduction taking place at the surface of conductive electrodes immersed in an electrolyte, under the influence of an applied potential. This process is used for reclaiming heavy metals from concentrated aqueous solutions. Application to waste water treatment may be limited because of cost factors. A frequent application is the recovery for recycle or reuse of metals, like copper, from waste streams. Pilot applications include oxidation of cyanide waste and separation of oil-water mixtures. Gaseous emissions may occur and, if they are hazardous and cannot be vented to the atmosphere, further treatment, such as scrubbing, is required. Waste water from the process may also require further treatment. 

Recently, new separation principles have been introduced and although these are very promising, they have not been extensively used for environmental analysis. Among them are FFF, pervaporation and biosorption. AU of them are easy to handle and not very expensive. In addition, FFF has very simple fundamental principles while pervaporation is very prone to automation and miniaturization. Biosorption is especially interesting for metal concentration because biosorbents can accumulate up to 25% of their dry weight in heavy metals. Some of the biosorbents are waste by-products of large scale industrial fermentations or certain abundant seaweeds. Analytes are easily released from the biosorbent and the biosorbent is regenerated for subsequent reuse. " ... 

Conventional physicochemical processes (neutralization, coagulation, flocculation, precipitation, and filtration) have been traditionally employed for the treatment before disposal of waste acid solutions containing heavy metals. However, they often fail to reduce the eoncentration of these pollutants below the permissible limits. Furthermore, these technologies usually do not provide the necessary selectivity to create valuable product streams suitable for recycling or reuse, and... 

Segregation of Waste Streams — The segregation of waste streams permits recovery of heavy metals, caustic recovery and reuse, and control of toxic spills (such as dieldrin used for moth-proofing). Many of the older textile mills have a common collection system with chemical reuse, but the modem mills have a segregated collection system to permit chemical recovery and reuse. 

The metal finishing industiy commonly uses alkaline cyanide plating baths to deposit copper and other heavy metals. The cyanides are extremely toxic to aquatic life and must be removed from the waste rinse water prior to discharge into waterways. Also, it is increasingly getting more attractive to recover the plating rinse solutions for reuse. 

---