Cationic heavy metals

From Morgan and Stumm, 1991. A = type A metal cation, nonheavy metals T = transition-metal cation (various oxidation states) B = type B metal cation, heavy metals GA = generally anionic (U.S. EPA, 1980a). 

Cadmium leached much more readily than the other metals and may have been bound by a different mechanism, possibly by particle surface adsorption rather than by tight complexation. Cadmium was the most soluble cationic heavy metal used in this experiment. It desorbs at higher pH and is less tightly adsorbed than chromium or lead. It was first detected in the fourth... 

UV/Vis detection with or without postcolumn derivatization UV/Vis light absorption UV active anions and cations, heavy metals after reaction with PAR and Tiron, polyvalent anions after reaction with iron(III), silicate and phosphate after reaction with molybdate, alkaline-earth metals after reaction with Arsenazo I... 

Ion-selective membranes attain their permselectivity from ion-exchange, dissolution, or complexation phenomena. Different types of membranes are available for the construction of ion-selective electrodes glass and other solid state rods (crystals), liquid or polymer ion ecchangers, or dissolved ionophores. Many electrodes are commercially available with selec-tivities for different ions, mainly H, alkali metal cations, heavy metal ions, and halides or pseudohalides. Also gas-sensing electrodes may be constructed from an ion-selective electrode and a gas-permeable membrane [182]. Ion selective electrodes and gas-selective electrodes... 

Inorganic pollutants include (a) cationic heavy metals such as lead, cadmium, and nickel, (b) anionic metals and inorganics such as arsenic, chromium, selenium, nitrate and fluoride, and (c) radionuclides such as strontium and uranium. The geochemistry of these pollutants can widely vary and it depends on the specific pollutant type and soil/sediment properties. The speciation and transport of these pollutants also depend on the dynamic changes in the pH and redox potential of the soil that occurs under applied electric potential. The dominant transport process... 

The retention of heavy metal ions over birnessite (Mn02) surfaces and on Ti02 (the rutile phase) has been studied in an effort to understand the reaction mechanism [64], Various mechanisms have been proposed for the sorption of cationic heavy metals on oxide surfaces such as birnessite. The formation of surface precipitates prior to bulk precipitates has been observed using transmission electron microscopy [64]. At pH 5 and Al(III) concentration of 400 uM, a surface precipitate is observed on birnessite but not on Ti02. It is important to... 

Selectivity of ion-exchanger-based ISEIs can be modified by adding an electrically neutral ionophore to the membranes (Figure 7. IB). Examples of ISEs based on commercially available neutral ionophores are summarized in Table 7.2. The neutral-ionophore-based electrodes were first developed using an antibiotic such as valinomycin as a K+-selective ionophore (K+-1). In addition to naturally occurring ionophores, many neutral iouophoies were synthesized for alkaline cations, alkaline earth cations, heavy metal ions, and inorganic anions. 

Cationic heavy-metal trapping Thiophene Japan 145,377 1975 Physical Research Institute... 

Soaps of heavy metals have been used but cationic surface-active agents have proved more suitable, notably organic amines of relatively high molecular weight. 

Anodic-stripping voltaimnetry (ASV) is used for the analysis of cations in solution, particularly to detemiine trace heavy metals. It involves pre-concentrating the metals at the electrode surface by reducmg the dissolved metal species in the sample to the zero oxidation state, where they tend to fomi amalgams with Hg. Subsequently, the potential is swept anodically resulting in the dissolution of tire metal species back into solution at their respective fomial potential values. The detemiination step often utilizes a square-wave scan (SWASV), since it increases the rapidity of tlie analysis, avoiding interference from oxygen in solution, and improves the sensitivity. This teclmique has been shown to enable the simultaneous detemiination of four to six trace metals at concentrations down to fractional parts per billion and has found widespread use in seawater analysis. 

It is thought that the function of the glue or gelatin is to combine with very slight traces of heavy metal cations, for example Cu, which are known to catalyse the nitrogen-forming reaction. 

Both the acid and its salts are powerful reducing agents. They reduce, for example, halogens to halides, and heavy metal cations to the metal. Copper(H) ion is reduced further to give copper(I) hydride, a red-brown precipitate ... 

Aminodiacetate exchangers have the —N(CH2COOH)2 group which has an unusually high preference for copper, iron, and other heavy metal cations and, to a lesser extent, for alkaline earth... 

Orthophosphate salts are generally prepared by the partial or total neutralization of orthophosphoric acid. Phase equiUbrium diagrams are particularly usehil in identifying conditions for the preparation of particular phosphate salts. The solution properties of orthophosphate salts of monovalent cations are distincdy different from those of the polyvalent cations, the latter exhibiting incongment solubiUty in most cases. The commercial phosphates include alkah metal, alkaline-earth, heavy metal, mixed metal, and ammonium salts of phosphoric acid. Sodium phosphates are the most important, followed by calcium, ammonium, and potassium salts. 

New chelating ion-exchange resins are able to selectively remove many heavy metals in the presence of high concentrations of univalent and divalent cations such as sodium and calcium. The heavy metals are held as weaMy acidic chelating complexes. The order of selectivity is Cu > Ni > Zn > Co > Cd > Fe + > Mn > Ca. This process is suitable for end-of-pipe polishing and for metal concentration and recovery. 

Chelant Control. Chelants are the prime additives in a solubilizing boiler water treatment program. Chelants have the abihty to complex many cations (hardness and heavy metals under boiler water conditions). They accomplish this by locking metals into a soluble organic ring stmcture. The chelated cations do not deposit in the boiler. When apphed with a dispersant, chelants produce clean waterside surfaces. 

The first synthetic organic pigments were used to shade or tone the weaker colorants and became known as toners. Metal toners usually contain one sulfonic acid group and often a carboxyUc acid group. The pigment is rendered iasoluble, ie, laked Ai a heavy metal cation. An example of a calcium salt is Lithol Rubine BK [5858-81-1] Vhl) (Cl Pigment Red 57 Cl 15850). 

Alcohols react with boric acid with elimination of water to form borate esters, B(OR)3. A wide variety of borate salts and complexes have been prepared by the reaction of boric acid and inorganic bases, amines, and heavy-metal cations or oxyanions (44,45). Fusion with metal oxides yields... 

In a study of the adsorption of soap and several synthetic surfactants on a variety of textile fibers, it was found that cotton and nylon adsorbed less surfactant than wool under comparable conditions (59). Among the various surfactants, the cationic types were adsorbed to the greatest extent, whereas nonionic types were adsorbed least. The adsorption of nonionic surfactants decreased with increasing length of the polyoxyethylene chain. When soaps were adsorbed, the fatty acid and the aLkaU behaved more or less independently just as they did when adsorbed on carbon. The adsorption of sodium oleate by cotton has been shown independently to result in the deposition of acid soap (a composition intermediate between the free fatty acid and the sodium salt), if no heavy-metal ions are present in the system (60). In hard water, the adsorbate has large proportions of lime soap. 

Despite the weak basicity of isoxazoles, complexes of the parent methyl and phenyl derivatives with numerous metal ions such as copper, zinc, cobalt, etc. have been described (79AHC(25) 147). Many transition metal cations form complexes with Imidazoles the coordination number is four to six (70AHC(12)103). The chemistry of pyrazole complexes has been especially well studied and coordination compounds are known with thlazoles and 1,2,4-triazoles. Tetrazole anions also form good ligands for heavy metals (77AHC(21)323). 

Heavy metals Cation Polystyrene matrix Chelating functional groups Mineral acids... 

POLYURETHANE FOAM MODIFIED WITH HETEROPOLYACIDS ARE THE NEW SORBENTS FOR ONECHARGED CATIONS OF HEAVY METALS... 

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