Mineral chelating agents

Generally, soluble materials are more effective as micronutrient sources than are insoluble ones. For this reason, many soil minerals that contain the micronutrient elements are ineffective sources for plants. Some principal micronutrient sources and uses are summarized below. In this discussion the term frits refers to a fused, pulverized siUceous material manufactured and marketed commercially for incorporation in fertilizers. Chelates refers to metaHoorganic complexes specially prepared and marketed as especially soluble, highly assimilable sources of micronutrient elements (see CHELATING agents). 

Mineral oil and paraffins should not be used, because these are not metabolized and may irritate tissue. Various other additives are needed for stabiUty, stefihty, and isotonicity antimicrobial preservatives, antioxidants (qv), chelating agents (qv), and buffers. No parenteral container material is completely inert to parenteral solvent systems. 

EDA reacts with formaldehyde and sodium cyanide under the appropriate alkaline conditions to yield the tetrasodium salt of ethylenediaminetetraacetic acid (24). By-product ammonia is removed at elevated temperatures under a partial vacuum. The free acid or its mono-, di-, or trisodium salts can be produced by the appropriate neutrali2ation using a strong mineral acid. This same reaction with other amines is used to produce polyamino acetic acids and their salts. These products are used widely as chelating agents. 

Treatment additives, chelating agents, and clay minerals can be added to a system to bind to metals and reduce metal mobility. Treatment additives, such as carbonates, phosphates, and hydroxides, form insoluble precipitates with metals, thus decreasing their bioavailability. Jonioh et al.141... 

In the case of mordenite, aluminum was solubilized in the two-step process primarily with mineral acids (5), while in the case of Y zeolites it involved acids (28,29), bases (17) or salts (30,31). The use of chelating agents has also been reported (32). 

Chelating agents that can form insoluble, hydrophobic chelates on the surface of minerals are potential collectors for the selective flotation of minerals.3 4 As early as 1927, Vivian5 reported the use of cupferron, a well-known analytical reagent, as a collector for the flotation of cassiterite (Sn02). Since then, there have been a number of reports on the use of chelating agents in flotation. 

Americium sorption was decreased significantly when HEDTA or EDTA were present. Complexation of americium by these strong chelating agents was responsible for this behavior. Sodium hydroxide increased americium sorption but, again, its effect on americium was probably a manifestation of its effect on the sediment minerals. 

Hydroxyapatite is not stable in the presence of chelating agents and at pH below 5 Both phenomena contribute to the degradation of the mineral structure and to partial or total dissolution of the crystals. 

Because of their large surface-to-volume ratio and high metabolic activity, microorganisms are important vectors in the introduction of heavy metal and radionuclide pollutants into food webs. As discussed in Chapter 5, heavy metals in soils and sediments tend to be immobilized by precipitation at neutral to alkaline pH and/or adsorption to cation exchange sites of clay minerals. Microbial production of acid and chelating agents can reverse this adsorption and mobilize toxic metals. Microbial metabolism products that can chelate metals include... 

The susceptibility of metal oxides to reduction and dissolution depends on mineralogy, crystallinity, surface area, the effectiveness of reducing and chelating agents, and microbial activity. Early culture studies with Ee(Hl)-respiring bacteria demonstrated that Ee(lll) reduction rates vary with mineral form or crystallinity... 

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