Seawater potassium

Potassium (K) is the seventh most abundant element on earth. It s found in silicate rocks and in seawater (potassium makes up about 0.04 percent of sea water). The symbol K comes from the Arabic term kalium, which is an abbreviation of al qili (alkaline). 

Other potential sources of potassium include insoluble minerals and ores, and the oceans, which contain 3.9 x 10 t/(km) of seawater (see Ocean RAW materials). The known recoverable potash reserves are sufficient for more than 1000 years at any foreseeable rate of consumption. 

Preparation and Manufacture. Magnesium chloride can be produced in large quantities from (/) camalhte or the end brines of the potash industry (see Potassium compounds) (2) magnesium hydroxide precipitated from seawater (7) by chlorination of magnesium oxide from various sources in the presence of carbon or carbonaceous materials and (4) as a by-product in the manufacture of titanium (see Titaniumand titanium alloys). 

The addition of 2,2, 4,4, 6-pentanitro-6 -methyldiphenylamine [64653-47-0] to seawater precipitates potassium (38). Aromatic amines, especially aminotetrahydronaphthalenes and their A[-aryl derivatives, are efficient flotation agents for quartz. The use of DPA for image formation in films has been patented (39,40). Diarylamines are used as intermediates (41) for azo, sulfur, oxidative base, triaryhnethane, oxazine, nitro, and safranine dyes (see Dyes and DYE INTERLffiDIATES). 

Seafood. Sorbates are used to extend the shelf life of many seafood products, both fresh and processed (103,104). For smoked or dried fish, an instantaneous dip in 5 wt % potassium sorbate or a 10-minute dip in 1.0 wt % potassium sorbate prior to drying or smoking inhibits the development of yeast and mold (105,106). For fresh fish, sorbates can be incorporated at approximately 0.5 wt % into the ice, refrigerated seawater, or ice-water slush in... 

Chlorine. Chlorine, the material used to make PVC, is the 20th most common element on earth, found virtually everywhere, in rocks, oceans, plants, animals, and human bodies. It is also essential to human life. Eree chlorine is produced geothermally within the earth, and occasionally finds its way to the earth s surface in its elemental state. More usually, however, it reacts with water vapor to form hydrochloric acid. Hydrochloric acid reacts quickly with other elements and compounds, forming stable compounds (usually chloride) such as sodium chloride (common salt), magnesium chloride, and potassium chloride, all found in large quantities in seawater. 

Seawater. Salt extraction from seawater is done by most countries having coastlines and weather conducive to evaporation. Seawater is evaporated in a series of concentration ponds until it is saturated with sodium chloride. At this point over 90% of the water has been removed, and some impurities, CaSO and CaCO, have been crystallized. This brine, now saturated in NaCl, is transferred to crystallizer ponds where salt precipitates on the floor of the pond as more water evaporates. Brine left over from the salt crystallizers is called bitterns because of its bitter taste. Bitterns is high in MgCl2, MgSO, and KCl. In some isolated cases, eg, India and China, magnesium and potassium compounds have been commercially extracted, but these represent only a small fraction of total world production. 

Table 8 5 shows that each of the four common s-block ions is abundant not only in seawater but also in body fluids, where these ions play essential biochemical roles. Sodium is the most abundant cation in fluids that are outside of cells, and proper functioning of body cells requires that sodium concentrations be maintained within a narrow range. One of the main functions of the kidneys is to control the excretion of sodium. Whereas sodium cations are abundant in the fluids outside of cells, potassium cations are the most abundant ions in the fluids inside cells. The difference in ion concentration across cell walls is responsible for the generation of nerve impulses that drive muscle contraction. If the difference in potassium ion concentration across cell walls deteriorates, muscular activity, including the regular muscle contractions of the heart, can be seriously disrupted. 

Schnepfe [83] has described yet another procedure for the determination of iodate and total iodine in seawater. To determine total iodine 1 ml of 1% aqueous sulfamic acid is added to 10 ml seawater which, if necessary, is filtered and then adjusted to a pH of less than 2.0. After 15 min, 1 ml sodium hydroxide (0.1 M) and 0.5 ml potassium permanganate (0.1M) are added and the mixture heated on a steam bath for one hour. The cooled solution is filtered and the residue washed. The filtrate and washings are diluted to 16 ml and 1ml of a phosphate solution (0.25 M) added (containing 0.3 xg iodine as iodate per ml) at 0 °C. Then 0.7 ml ferrous chloride (0.1 M) in 0.2% v/v sulfuric acid, 5 ml aqueous sulfuric acid (10%) - phosphoric acid (1 1) are added at 0 °C followed by 2 ml starch-cadmium iodide reagent. The solution is diluted to 25 ml and after 10-15 min the extinction of the starch-iodine complex is measured in a -5 cm cell. To determine iodate the same procedure is followed as is described previously except that the oxidation stage with sodium hydroxide - potassium permanganate is omitted and only 0.2 ml ferrous chloride solution is added. A potassium iodate standard was used in both methods. 

Eberlein and Kattner [194] described an automated method for the determination of orthophosphate and total dissolved phosphorus in the marine environment. Separate aliquots of filtered seawater samples were used for the determination orthophosphate and total dissolved phosphorus in the concentration range 0.01-5 xg/l phosphorus. The digestion mixture for total dissolved phosphorus consisted of sodium hydroxide (1.5 g), potassium peroxidisulfate (5 g) and boric acid (3 g) dissolved in doubly distilled water (100 ml). Seawater samples (50 ml) were mixed with the digestion reagent, heated under pressure at 115-120 °C for 2 h, cooled, and stored before determination in the autoanalyser system. For total phosphorus, extra ascorbic acid was added to the aerosol water of the autoanalyser manifold before the reagents used for the molybdenum blue reaction were added. For measurement of orthophosphate, a phosphate working reagent composed of sulfuric acid, ammonium molyb-... 

Wong [8] found that the determination of residual chlorine in seawater by the amperometic titrimetic method, potassium iodide must be added to the sample before the addition of the pH 4 buffer, and the addition of these two reagents should not be more than a minute apart. Serious analytical error may arise if the order of addition of the reagents is reversed. There is no evidence suggesting the formation of iodate by the reaction between hypobromite and iodide. Concentrations of residual chlorine below 1 mg/1 iodate, which occurs naturally in seawater, causes serious analytical uncertainties. 

In another spectrophotometric procedure Motomizu [224] adds to the sample (2 litres) 40% (w/v) sodium citrate dihydrate solution (10 ml) and a 0.2% solution of 2-ethylamino-5-nitrosophenol in 0.01 M hydrochloric acid (20 ml). After 30 min, add 10% aqueous EDTA (10 ml) and 1,2-dichloroethane (20 ml), mechanically shake the mixture for 10 minutes, separate the organic phase and wash it successively with hydrochloric acid (1 2) (3 x 5 ml), potassium hydroxide (5 ml), and hydrochloric acid (1 2) (5 ml). Filter, and measure the extinction at 462 nm in a 50 mm cell. Determine the reagent blank by adding EDTA solution before the citrate solution. The sample is either set aside for about 1 day before analysis (the organic extract should then be centrifuged), or preferably it is passed through a 0.45 xm membrane-filter. The optimum pH range for samples is 5.5 - 7.5. From 0.07 to 0.12 p,g/l of cobalt was determined there is no interference from species commonly present in seawater. 

In a method described by Kiriyama and Kuroda [500], molybdenum is sorbed strongly on Amberlite CG 400 (Cl form) at pH 3 from seawater containing ascorbic acid, and is easily eluted with 6 M nitric acid. Molybdenum in the effluent can be determined spectrophotometrically with potassium thiocyanate and stannous chloride. The combined method allows selective and sensitive determination of traces of molybdenum in seawater. The precision of the method is 2% at a molybdenum level of 10 xg/l. To evaluate the feasibility of this method, Kiriyama and Kuroda [500] spiked a known amount of molybdenum and analysed it by this procedure. The recoveries for 4 to 8 xg molybdenum added to 500 or 1000 ml samples were between 90 and 100%. 

Nakahara and Chakrabarti [137] showed that the seawater salt matrix can be removed from the sample by selective volatilisation at 1700-1850 °C, but the presence of sodium chloride, sodium sulfate, and potassium chloride causes a considerable decrease in molybdenum absorbance, and magnesium chloride and calcium chloride cause a pronounced enhancement. The presence of magnesium chloride prevents the depressive effects. Samples of less than 50 pi can be analysed directly without using a background corrector with a precision of 10%. 

Potentiometric titration has been applied to the determination of potassium in seawater [532-534], Torbjoern and Jaguer [533-544] used a potassium selective valinomycin electrode and a computerised semiautomatic titrator. Samples were titrated with standard additions of aqueous potassium so that the potassium to sodium ion ratio increased on addition of the titrant, and the contribution from sodium ions to the membrane potential could be neglected. The initial concentration of potassium ions was then derived by the extrapolation procedure of Gran. 

Marquis and Lebel [534] precipitated potassium from seawater or marine sediment pore water using sodium tetraphenylborate, after first removing halogen ions with silver nitrate. Excess tetraphenylborate was then determined by silver nitrate titration using a silver electrode for endpoint detection. The content of potassium in the sample was obtained from the difference between the amount of tetraphenyl boron measured and the amount initially added. 

Polarography has also been applied to the determination of potassium in seawater [535]. The sample (1 ml) is heated to 70 °C and treated with 0.1 M sodium tetraphenylborate (1 ml). The precipitated potassium tetraphenylborate is filtered off, washed with 1% acetic acid, and dissolved in 5 ml acetone. This solution is treated with 3 ml 0.1 M thallium nitrate and 1.25 ml 2M sodium hydroxide, and the precipitate of thallium tetraphenylborate is filtered off. The filtrate is made up to 25 ml, and after de-aeration with nitrogen, unconsumed thallium is determined polarographically. There is no interference from 60 mg sodium, 0.2 mg calcium or magnesium, 20 pg barium, or 2.5 pg strontium. Standard eviations at concentrations of 375, 750, and 1125 pg potassium per ml were 26.4, 26.9, and 30.5, respectively. Results agreed with those obtained by flame photometry. 

Muzzarelli and Sipos [622] showed that a column of chitosan (15 x 10 mm) can be used to concentrate zinc from 3 litres of seawater before determination by anodic-stripping voltammetry with a composite mercury-graphite electrode. Zinc (and lead) are eluted from the column by 2 M ammonium acetate (50 ml), copper by 0.01 M EDTA (10 ml), and cadmium by 0.1 M potassium cyanide (3 ml). 

Riley and Taylor [39] have studied the uptake of about 30 organics from seawater onto the resin at pH 2 - 9. At the 2 - 5 p,g/l level none of the carbohydrates, amino acids, proteins or phenols investigated were adsorbed in any detectable amounts. Various carboxylic acids, surfactants, insecticides, dyestuffs, and especially humic acids are adsorbed. The humic acids retained on the XAD-1 resin were fractionated by elution with water at pH 7, M aqueous ammonia, and 0.2 M potassium hydroxide. 

Crisp et al. [212] has described a method for the determination of non-ionic detergent concentrations between 0.05 and 2 mg/1 in fresh, estuarine, and seawater based on solvent extraction of the detergent-potassium tetrathiocyana-tozincate (II) complex followed by determination of extracted zinc by atomic AAS. A method is described for the determination of non-ionic surfactants in the concentration range 0.05-2 mg/1. Surfactant molecules are extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozin-cate (II), and the determination is completed by AAS. With a 150 ml water sample the limit of detection is 0.03 mg/1 (as Triton X-100). The method is relatively free from interference by anionic surfactants the presence of up to 5 mg/1 of anionic surfactant introduces an error of no more than 0.07 mg/1 (as Triton X-100) in the apparent non-ionic surfactant concentration. The performance of this method in the presence of anionic surfactants is of special importance, since most natural samples which contain non-ionic surfactants also contain anionic surfactants. Soaps, such as sodium stearate, do not interfere with the recovery of Triton X-100 (1 mg/1) when present at the same concentration (i.e., mg/1). Cationic surfactants, however, form extractable nonassociation compounds with the tetrathiocyanatozincate ion and interfere with the method. 

Yamamoto et al. [60] determined picogram quantities of methyl mercury and total mercury in seawater by gold amalgamation and atomic absorption spectrometry. Methyl mercury was extracted with benzene and concentrated by a succession of three partitions between benzene and cysteine solution. Total mercury was extracted by wet combustion of the sample with sulfuric acid and potassium permanganate. The proportion of methyl mercury to total mercury in the coastal seawater sampled was around 1%. 

Schnepfe [4] has described a method for the determination of total iodine and iodate in seawater. One per cent aqueous sulfamic acid (1 ml) is added to seawater (10 ml), then it is filtered, if necessary, and the pH adjusted to 2. After 15 min, 1 ml 0.1 M sodium hydroxide and 0.5 ml 0.1 M potassium permanganate are added and the steam bath heated for 1 h. The cooled solution is filtered, the residue washed, the filtrate plus washings is diluted to 16 ml and 1 ml of a 0.25 M phosphate solution (containing 0.3 pg iodine as IOj per... 

---