Waste acid neutralisation

Mining wastes and overburden. Estonian kukersite oil shales occur in limestone strata (Schmidt 1858, 1881), yielding a carbonate-rich spoil with significant potential for acid neutralisation. Other oil shales, for example, the siliceous Estonian Dictyo-nema shales, which contain only traces of carbonate compared with the kukersites, are associated with sulphides, such as pyrite, and may thus generate acidic leachate due to pyrite oxidation (Puura Pihlak 1998 Puura et al. 1999). 

Sulphonation with sulphuric acid or oleum is initially rapid and exothermic. The rate of reaction is highly dependent on the concentration of the sulphuric acid, so the reaction slows significantly as the sulphonating agent is consumed and further diluted by the water which is a by-product of the reaction. Processes based on sulphuric acid use large excesses, resulting in high levels of waste acid or residual sulphate in the neutralised product. An alternative is to remove the water from the reaction mixture, usually by two-phase distillation, with excess substrate as a carrier. 

The polymer industry requires large quantities of 4,4 -diaminodiphenyl-methanes. These compounds are used in various applications as polymer additives. Currently they are manufactured by the acid-catalysed condensation of anilines with formaldehyde but like so many reactions of this type, the processes require the neutralisation of waste acid leading to large amounts of salt waste. Cleaner processes are required and solid acids offer a way forward. One potentially useful example of this is the aqueous reaction of aromatic anilines adsorbed on kaolinite with formaldehyde which cleanly give the desired products (Figure 3.5).36 In a typical experiment, the clay is stirred with water before aniline is added to the stirred solution. To this is slowly added formaldehyde solution. The precipitated 4,4 -diaminodiphenylmethane can be extracted in hot ethanol in a yield of 96%. Similarly, several substituted analogues have been prepared in yields of 70-99%. 

Battery recycling creates lead-containing wastes which are classified as dangerous -in particular, smelting slag and slurries from sulphuric acid neutralisation. COBAT supervise the recyclers to ensure that they send this particular waste to landfill or use it according to the law. 

Commence simultaneous acid and caustic regeneration 6% HCl solution up flow through the cation bed for 30 min and 4% NaOH solution at 43—49°C downflow through the anion bed for 60 min. The two streams flow out to waste-water neutralisation tank through the interface collector imbedded in the inert resin layer. 

The sodium sulfate solution resulting from past desulfurisation can be filtered, evaporated and crystallised to produce sodium sulfate for sale. It is used in water treatment and for detergent manufacture as the quality from this source is sufficiently free of metals for this purpose. In the case where sodium carbonate is used the residual solution is usually neutralised with waste acid to remove any residual carbonate before evaporation and crystallisation. 

Medium 1 Medium 2 acidic waste water waste water neutralised with NaOH and lime milk ... 

The application of electrochemical neutralisation has been considered by Walther [11] to utilise waste acids and bases for elecfricity. In the invention of Walfher [11], the acid-base neutralisation voltage is superimposed to a Faraday cell of Ag/Ag20 electrode. The theoretical cell voltage of the acid-alkaline hybrid battery can be 0.95 V, as shown by the half-cell reactions 11.7 and 11.8, and the additional acid-base neutralisation reaction 11.9. 

V. G. Mosienko, Y. I. Petrakov, V. F. Nagomova, and V. N. Nikiforova. Complex additive for plugging solutions—contains modifying reagent in form of waste from production of sebacic acid, from stage of neutralising of sodium salts of fatty acids. Patent RU 2074310-C, 1997. 

However, because both acids and bases are used in cleaning, it may be possible to store these chemicals in a stirred buffer tank to allow the solution to neutralise. This solution may then may be slowly added to the concentrate waste to dilute it and allow for a safe disposal (Mauguin and Corsin 2005). Note that the volume of this discharge is much lower than both the concentrate and filter backwash discharges. 

Calcium oxide (CaO) is a base and is still used by some farmers to spread on fields to neutralise soil acidity and to improve drainage of water through soils that contain large amounts of clay. It is also used to neutralise industrial waste products, for example in flue... 

Calcium hydroxide is a cheap industrial alkali (Figure 13.9). It is used in large quantities to make bleaching powder, by some farmers to reduce soil acidity, for neutralising acidic industrial waste products, in the manufacture of whitewash, in glass manufacture and in water purification. Calcium hydroxide, in its white powder form, is produced by adding an equal amount of water to calcium oxide in a carefully controlled reaction. The control is needed because it is a very exothermic reaction. 

There are chemical explosion hazards associated with stored reprocessing residues. The explosion near Chelyabinsk in the Urals in 1958 was, it has been suggested, powered by interaction of sodium nitrate and/or nitric acid with sodium acetate/acetic acid in nitrate wastes neutralised with sodium acetate, then stored and allowed to concentrate by radioactive heating [1]. A reprocessing incident at Tomsk in 1993 was apparently caused... 

The technological process of the biochemical purification of waste waters in silicone production comprises the following stages the neutralisation of acid waste waters the averaging and mechanical purification of waste waters the biochemical purification of waste waters and the dehydration of the sediment (Fig. 82). 

Acid waste waters from silicone production enter neutraliser 9, a concrete container with two agitators, lined with acid-resistant tile from epoxy resin. Here the waste waters are neutralised with lime milk, which is automatically sent from reservoirs 6 with pumps 8. The pumps automatically switch off when pH in the neutraliser is 8-10 and switch on when pH is below 5. Neutral waste waters continuously self-flow through a collector into receiving reservoir 10 as they accumulate, they are automatically sent with pumps 11 for averaging and mechanical purification. 

Liquid acidic wastes from the process were neutralised to form solid gypsum that was then sold to the building, paper and farming industries. The gaseous effluent, carbon dioxide, was sold to the beer and beverage industries. Finally, the iron salts were isolated and sold to the water treatment industry. In 1994 some 580000 tonnes of these products were sold to these industries. 

Ferric oxide is also prepared from liquors containing ferric salts in solution, and which are otherwise waste products in many manufacturing processes. If ferrous salts are present, they are first oxidised by addition of nitric acid or bleaching powder. The acid is neutralised by addition of soda or lime, ferric hydroxide being precipitated. The washed product is finally dehydrated by heat, becoming perfectly anhydrous at 500° C. upwards.5... 

A basic ferric sulphate under the name of chemical sand is used commercially to neutralise the alkali present in waste soap lyes from which the glycerine is to be recovered. It is manufactured by mixing dry and finely powdered iron ore (oxide) with concentrated sulphuric acid, and allowing the fluid mass to spread out on an iron floor. When solidification has taken place, the mass is broken up and heated at a temperature of 200° to 280° C. for some hours, when it is ready for use, and consists essentially of ferric oxide and ferric sulphate.10... 

Land reclamation. Lime stabilisation is being used in the reclamation of a wide range of derelict sites. Not only does the lime stabilise pozzolanic material on the site, but it helps to neutralise acidic residues, immobilise heavy metals and saponify oily wastes. It can also be used to dry out a site to enable piling equipment to be brought in, or to assist with the removal of sludges. 

The type and concentration of the acid(s) can have a marked effect on the neutralisation process, largely owing to the solubility of the reaction product(s). The acids most commonly found in waste water are nitric (HNO3), hydrochloric (HCl), sulfuric (H2SO4), hydrofluoric (HF) and phosphoric (H3PO4). The solubilities of their calcium and magnesium salts are summarised in Table 28.6 [28.7] (N.B., all sodium salts are soluble). 

Residues from processing citrus fruits are mixed with lime, dried, and sold as cattle feed. Lime is also used to neutralise waste citric acid and to raise the pH of fruit juices to stabilise the flavour and colour [30.1]. 

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