Heavy metals from liquid waste

TABLE 3.4 Processes That Separate Heavy Metals from Liquid Waste Streams... 

Aqueous systems have been used in separations, coatings, and synthesis. Aqueous biphasic systems have been developed for hquid-liquid extractions using water-soluble polymers such as polyethylene glycol, and inorganic salts such as ammonium chloride or potassium phosphate (Rogers et al., 1998), (Sherman et al., 1998). These systems have been investigated for use in the separation and recovery of heavy metals from mixed wastes and in the recovery of colored impurities from textile waste streams (Sherman et al., 1998). 

Flocculation and sedimentation arc two processes used to separate waste streams that contain both a liquid and a solid phase. Both are well-developed, highly competitive processes, which arc oflcii used in the complete treatment of waste streams. They may also be used instead of, or in addition to, filtration. Some applications include the removal of suspended solid particles and soluble heavy metals from aqueous streams. Many industries use both processes in the rcmowal of pollutants from their wastewaters. These processes work best when the waste stream contains a low concentration of the contaminating solids. Although they are applicable to a wide variety of aqueous waste streams, these processes arc not generally used to treat nonaqueous or semisolid waste streams such as sludges and slurries. 

Boyadzhiev L. Extraction of heavy metals from waste waters hy liquid membrane techniques. J Environ Prot Ecol, 2000 1(1) 72-80. Alexandrova S, Saboni A, Boyadzhiev L, Mouhah N, and Estel L. Recovery of substances by rotating-film pertraction. Chem Eng... 

The processes that can be used to separate heavy metals from industrial liquid waste streams are given in Table 3.4, processes that can treat various tars or solids are shown in Table 3.5, and processes suitable for treating slurries and sludges are listed in Table 3.6. 

The Landmark diatomite material is treated and processed to a purity and grade that will collect angstrom-sized particles. According to the vendor, because of the diversity and shapes of the diatoms, different blends may be formulated to filter out almost any kind of material from a liquid including heavy metals, organics, and radionuclides from low-level waste streams of nuclear installations. 

Pozzolanic S/S has many varied applications in the field. It has been found to be a fast, simple, and low-cost measure for the treatment of a variety of wastes. It has been used for treating solids, liquids, sediments, and sludges from several industries, particularly those that produce heavy-metal-contaminated waste streams, and especially at sites where the soil contains lead. 

In 1984 the Hazardous and Solid Waste Amendments to the Resource and Conservation Act of 1976 (RCRA) were passed prohibiting the land disposal of certain hazardous wastes. Among these amendments is the "California List" distinguishing hazardous wastes now banned from landfilling such as liquid wastes containing greater than 20 mg/1 mercury. This waste is subject to the treatment requirements for heavy metals which are metal recovery or solidification (40 CFR 268.7 (a) and 268.7 (b)). ... 

The liquid from spent caustic soda baths must be disposed of or treated as a hazardous waste. The finish residue may contain heavy metals as well as caustic thus requiring treatment as a hazardous waste,... 

Apart from radioactive compounds the radioactive wastes may contain non-active but chemically toxic substances. The national standards and regulations describe the discharge limits for these substances, too. Heavy metals are toxic compounds, most often present in liquid radioactive wastes. The experiments showed that most of these metals are removed by UF/complexation method. The method is inefficient for removal of monovalent ions, bivalent cations and anions are retained in 25%-50%, but high retention of the metals like Mn, Fe, Co, Cu, Pb, Cr was observed. The retention factors for those metals in two-stage experiment described above, were as follows ... 

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