Brine sulphate removal

Capital and operating costs are low, offering a short payback in comparison to conventional methods of sulphate removal such as brine purge and barium or calcium precipitation. 

It should be noted that the operating parameters of the unit can be adjusted to suit the client s needs. These particular operating conditions were an attempt to maximise productivity (i.e. minimise capital cost) and minimise the waste volume. While the NaCl recovery efficiency is about 96%, the brine purity is not exceptionally good (43.4% sulphate removal). This is not considered a disadvantage, however, since the low removal efficiency can be compensated for by increasing the flow of feed that is treated by the system. If necessary, removal efficiencies of over 95 % can be obtained. 

Matsushita, T. (1996) Sulphate removal from brine by using amphoteric ion exchange resin. Journal of Ion Exchange, 7(3), 36—43. 

Kvaerner Chemetics have developed a novel, patented process [1] for the removal of multivalent anions from concentrated brine solutions. The prime market for this process is the removal of sodium sulphate from chlor-alkali and sodium chlorate brine systems. The sulphate ion in a brine solution can have a detrimental effect on ion-exchange membranes used in the production of chlorine and sodium hydroxide consequently tight limits are imposed on the concentration of sulphate ions in brine. As brine is continuously recycled from the electrolysers back to the saturation area, progressively more and more sulphate ions are dissolved and build up quickly in concentration to exceed the allowable process limits. A number of processes have been designed to remove sulphate ions from brine. Most of these methods are either high in capital or operating cost [2] or have large effluent flows. 

Maycock, K., Twardowski, Z. Ulan, J. (1998) A new method to remove sodium sulphate from brine. In Modern Chlor-alkali Technology, Vol. 7, pp 220-221. The Society of Chemical Industry, London and Royal Society of Chemistry, London. 

Process to Remove Sulphate, Iodide and Silica from Brine... 

This chapter introduces applications of RNDS to the removal of sulphate, iodide and silica from brine. 

When ion-exchange resin containing zirconium hydroxide comes into contact with acidic brine in the RNDS , zirconium hydroxide adsorbs bisulphate ions thus sulphate is removed from brine. For regeneration of the ion-exchange resin, a basic solution is supplied and when it comes into contact with the resin, sulphate desorption starts. 

As was mentioned previously, an effective system, RNDS , has been developed to remove particular impurities from brine used in membrane electrolysis procedures. The basic concept of RNDS is to bring the feed brine into contact with an ion-exchange resin containing zirconium hydroxide for the adsorptive removal of impurities. For the removal of the sulphate ion from brine, commercial plants utilising RNDS are already in service. For the elimination of iodide and silica, pilot-scale testing is being planned. 

Novel ion-exchange technology has recently been developed for purification of brine. Different resins have been developed for removal of sulphate impurities as well as calcium and magnesium hardness. The process is very simple and since only water is consumed to regenerate the ion-exchange resins, the operating costs are extremely low. The equipment, which is similar to that currently widely utilised for purification of waste acid, is very compact. It is expected that commercial-scale systems of both types will be installed later in 2000. 

Minz, F.R. (1985) Process for removing sulphate from electrolysis brine. United States Patent No. 4,556,463. 

Brines are also cone, by evaporation under reduced press., i.e. in what are called vacuum fans heated by steam, and specially designed to eliminate difficulties arising from the tendency of the brine to deposit a hard scale or crust of calcium salts. In some cases, the magnesium salts are first precipitated as magnesium hydroxide, Mg(OH)2, by the addition of milk of lime, and the calcium sulphate subsequently removed by precipitation as carbonate by the addition of ammonium carbonate liquors. The decanted liquor is then cone, in vacuum pans. 

When the brines are vary weak, they are always mado to undergo a preliminary evaporation in the air and when the presence of sulphates and the chlorides of calcium and magnesium are calculated hy their quantity to Impair the commercial character of the product, certain purifying processes are had recourse to by which. these are removed. When, earhonate of iron is present in the weak brine, it is generally got rid of by exposing the brine for some time to the air. The carbonic acid by which the Iron is bald in solution gradually escapes... 

To a stirred suspension of diisopinocampheylborane (50 mmol) (1) in tetra-hydrofuran (18 ml) is added 4.5 ml of (Z)-but-2-ene. The reaction mixture is stirred at 25 °C for 4.5 hours. The solid diisopinocampheylborane disappears and the formation of the trialkylborane is complete. The organoborane is treated with 4 ml of methanol, followed by 18.3 ml of 3 m sodium hydroxide and the careful addition of 20 ml of 30 per cent hydrogen peroxide, maintaining the temperature of the reaction below 40 °C. The reaction mixture is further stirred at 55 °C for 1 hour, cooled, and extracted with ether (3 x 50 ml). The extract is washed successively with water (2 x 25 ml) and brine (3 ml) and dried over magnesium sulphate. The organic layer is carefully fractionated to provide butan-2-ol, b.p. 96-98 °C, 2.9 g (73%), purity > 95 per cent. The last traces of impurities are removed by preparative g.l.c. (2) to yield (R)-butan-2-ol, [a] 3 —13.23° (neat), ee 98.1 per cent. 

Dimethyl 2-methylenepentanedioate. Methyl acrylate (30.0 g, 349 mmol) (distilled immediately before use) and dry pyridine (30 ml, CAUTION) containing tris(cyclohexyl)phosphine-carbon disulphide complex (2.0 g, 6 mmol) (1) are refluxed under nitrogen for 16 hours. The deep red solution is cooled and the pyridine removed under reduced pressure. The residue is taken up in ether (400 ml) and the solution washed with aqueous 1 m hydrochloric acid (3 x 40 ml). The combined aqueous layers are extracted with ether (2 x 50 ml) and the combined organic layers washed with 1 m hydrochloric acid (30 ml), saturated brine (40 ml) and saturated aqueous sodium hydrogen carbonate (2 x 30 ml), dried over sodium sulphate and evaporated. Distillation of the oil gives dimethyl 2-methylenepentanedioate (23.8 g, 79%) as a liquid, b.p. 66-68 °C/1 mmHg i.r. (thin film) 1738, 1715, 1635cm-1. 

Portion 2 The mixture was evaporated to give an oil which was taken up in chloroform (200 ml) then washed with water (100 ml). The chloroform solution was washed with brine (100 ml), dried over magnesium sulphate, and then concentrated under reduced pressure at 45°C to give a brown oil. The oil was dissolved in acetone (200 ml) and activated charcoal (0.5 g) was added to the solution. The mixture was boiled under reflux for 10 minutes, then cooled to 45°C and filtered at this temperature to remove the charcoal. The filtrate was cooled to 20°C, seeded with nizatidine (0.05 g), then cooled 0°-5°C for 45 minutes during which time crystallisation occurred. The mixture was filtered to give nizatidine (9.4 g, 32.2%). 

When the brine is purified sulphate ions are also removed as they increase the anodic evolution of oxygen by which graphite losses are raised. 

This dechlorination method is not considerably applied in practice as it entails the consumption of a certain amount of alkali hydroxide and also all the dissolved chlorine is depreciated by conversion to chloride. Therefore, this method is sometimes used for removing the last remnants of chlorine from the brine which has previously been dechlorinated by evacuation and aeration instead of the method using sodium bisulphite and sulphur dioxide because in this case undesirable sulphate ions are formed in the brine. 

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