Caustic occurrence

The chemical category of inorganic salts encompasses many substances that dissociate completely in water, but only one salt, sodium chloride, is referred to by the common name, salt. Sodium chloride is ubiquitous in both its occurrence and its many uses. To date, there are over 14,000 uses for salt.1 Salt is used as a feedstock for many chemicals including chlorine, caustic soda (sodium hydroxide), synthetic soda ash (sodium carbonate), sodium chlorate, sodium sulfate, and metallic sodium. By indirect methods, sodium chloride is also used to produce hydrochloric acid and many other sodium salts. In its natural mineral form, salt may take on some color from some of the trace elements and other salts present, however, pure sodium chloride is a white to colorless crystalline substance, fairly soluble in water.2 Also known as halite, the substance... 

The removal of silica from a siliceous iron ore, such as the taconites found in Minnesota and Wisconsin, has been studied by Tiemann (T7, T9). Caustic concentrations from 25-500 gm/liter were used to digest the ore in a bomb at temperatures from 312 to 408°F. The leaching pressures in the bomb correspond closely to the equilibrium vapor pressures of the sodium hydroxide solutions used. A residual concentrate containing around 65% iron was obtained with —200 mesh material in 60 min of contact time. The high rate of dissolution of the silica was attributed to its occurrence in the form of microcrystalline (chalcedonic) varieties with high specific surface. The dissolution rate of pure quartz is directly proportional to the surface area and an average rate of 17 X 10 gm moles/cm sec was obtained for a 100 gm/liter NaOH solution at 312°F for the —400 mesh fraction. 

The Raney alloy... are leached in aqueous alkaline solutions to remove aluminum. The preferred solutions are dilute aqueous solution." of sodium or potassium hydroxide. Aluminum reacts with the aqueou. -caustic solution, resulting in the formation of hydrogen. If hot or concen trated solutions are used, reaction proceeds very rapidly with the immediate evolution of large quantities of hydrogen. This destroys the desired mechanical structure of the product. To prevent this occurrence, the leaching is instituted in relatively cool and dilute aqueous caustic solutions, i.e., initial room temperature leaching with solutions... 

Yamaguchi S, Matsumoto H, Hoshide M, et al. 1971. Occurrence of alkylmercury compound in caustic soda factory. Arch Environ Health 23 196-201. 

The described system has been deployed in a variety of real world venues across the United States to detemune theories of deployment and response and to verify robustness of the trigger and learning ability. To date over 120,000 hours of real world data has been collected. Several actual incidents have been recorded and learned. An example is the caustic over feed event depicted in Graph 3. Graph 4 shows a very noisy real world situation and demonstrates how quickly the system can learn commonly occurring unknown events to help reduce their occurrence. 

Caustic substances like strong acids, strong alkalis, bromine, chlorine gas, etc., are toxic because they dissolve and destroy tissue. Many accidents happen because of carelessness with such substances, but in ecotoxicology they are perhaps not so important. More interest is focused on electrophilic substances that may react with DNA and induce cancer. Such substances are very often formed by transformation of harmless substances within the body. Their production, occurrence, and protection mechanisms will be described in some detail later. 

Caustic Scrubbers and Sour-Water Strippers. Caustic scrubbers and sour-water strippers are used to remove sulfur from a variety of products, gases, and waste streams. Foaming is a fairly common occurrence in these systems because of contaminants found in the streams. 

Lithia is not quite so soluble in water as soda or potash, nor is it so caustic but it very much resembles these alkalies. Its solution attracts carbonic acid as readily as theirs from the atmosphere. When lithia is fused on platinum, it corrodes and stains the metal. Lithia and all its salts give a blood-red colour to flame. The carbonate of lithia is sparingly soluble, and its phosphate is nearly insoluble. Lithia occurs too rarely to admit of any useful application / but it is important to know that lithion-mica, which is recognised by its easy fusibility before the blow pipe, and by its tinging the outer flame red, has hitherto been only found associated with albite and topaz, or pycnite, in tin districts, and its occurrence, thus associated, may be looked on as a sure indication of the existence of tin in the locality. 

The main identified risks for these operations are the possible escape of sodium (with fire risk — although the sodium is low-temperature which reduces this risk), and the hydrogen risk generated by the transformation into caustic soda. A safety report evaluating these risks in detail and the counter-measures implemented to reduce their occurrence and consequences has been prepared in order to obtain the necessary authorizations from the DSEM. 

Stress-corrosion cracking of steel was first encountered in a practical way in riveted steam boilers. Stresses at rivets always exceed the elastic Unfit, and boiler waters are normally treated with alkalies to minimize corrosion. Crevices between rivets and boiler plate allow boiler water to concentrate, until the concentration of alkali suffices to induce S.C.C., sometimes accompanied by explosion of the boiler. Because alkalies were recognized as one of the causes, failures of this kind were first called caustic embrittlement. With the advent of welded boilers and with improved boiler-water treatment, S.C.C. of boilers has become less common. Its occurrence has not been eliminated entirely, however, because significant stresses, for example, may be established at welded sections of boilers or in tanks used for storing concentrated alkalies. 

Natural occurrence of magnesium in raw water enables fluoride removal due to formation of MgCOH) floes in the presence of lime. In this case, the water must be treated to a caustic alkalinity of 30 mg F-/L, a pH of >10.5 with option of recarbonation. Magnesia and calcined magnesite have also been tried for fluoride removal from water and their separation capacity was reported to improve with temperature. 

---