Evaporation Plant for Recycling of Caustic Soda

The present study discusses the cause of ground heave of an inherently non-swelling, kaolinite-rich red soil (from Bangalore, India) due to prolonged spillage of concentrated (40%, weight/weight solution) caustic soda (sodium hydroxide) solution into the sub-soil through cracked drains in an industrial establishment. The heave of the foundation soil caused considerable distress to the industrial building. The proposed remedial measures to chemically stabilize the contaminated foundation soil against future caustic soda solution spillage are also considered. The observed heave of the undisturbed soil sample in the laboratory oedometer test on permeation of 40% caustic soda solution and the significantly reduced pH of the outflowing caustic soda solution (pH = 9.35), suggested that certain chemical reactions occur during the passage of the strong alkali solution through the residual soil that is responsible for the ground heave. It is considered that loss of the cementitious iron oxide coatings coupled with the negative charge imparted to the soil particles by the passage of the caustic soda solution, disperse the soil particles that manifests as ground heave. Treatment of the contaminated ground with 5% ferric chloride solution and simultaneously taking measures to minimize caustic soda solution spillage should stabilize the foundation soil against heave from caustic soda attack for several years.

The recycling of caustic soda solution in aluminum processing is proposed in order to decrease the energy consumption and environmental impact. Methanol as an anti‐solvent in the caustic soda solution was found to be the most effective solvent for reducing gibbsite solubility. The gibbsite solubility in caustic soda was significantly reduced when methanol was added by more than 40 wt%. It was found that the gibbsite solubility with 55 w t% methanol was about a half of that without methanol. Methanol has low latent heat, and can be economically separated from the caustic soda solution. This recycling leads to an increase in the dissolution rate of alumina and/or aluminum, at atmospheric pressure, with a more concentrated caustic soda solution (up to 500 g/L NaOH). A more concentrated caustic soda solution can be recycled more economically, for example, that used in the die recovery process in aluminum forming plants. Optimization by the controlled addition or mixing of methanol in the caustic solution easily controls the growth rate and nucleation rate of gibbsite crystals in the crystallizer. Synergy of these advantages of the present recycling method may contribute to more cost effective operations, and minimization of environmental impacts from the disposal of spent caustic soda solution.

Influence of oxalic acid on the kinetics of Al(OH) 3 growth from caustic soda solutions

It is imperative to minimize radioiodine release to the environment through gaseous emissions of spent fuel reprocessing facilities, thereby mitigating its potential impact on the general public. One effective and widely adopted strategy for achieving this objective is caustic scrubbing, a method that involves the absorption of molecular iodine from gaseous streams using caustic soda ( NaOH ) solution in a packed column. In-depth laboratory-scale experiments were conducted to ascertain the overall volumetric mass transfer coefficient K G a for the absorption of dilute iodine vapor from air into a caustic soda solution in a packed column and to establish optimum performance parameters for this process. The investigation yielded noteworthy findings: K G a increased proportionately to (Gas phase Reynolds number)1.0 at constant liquid flow rates across all types of packing tested. K G a displayed relative independence from liquid velocities for high and moderate NaOH concentrations. However, this coefficient varied proportionately to (Liquid phase velocity)0.26 to 0.42 at lower NaOH concentrations under conditions of high gas flow rates NaOH . As the height of the column increased, K G a was found to decrease slightly. The presence of NOx at an inlet concentration of 9000 ppm in the gaseous stream led to a reduction in the mass transfer coefficient of iodine, particularly at low NaOH concentrations. In summary, the study underscores the importance of caustic scrubbing as an effective means to minimize the release of radioiodine. The investigation’s results provide valuable insights into optimizing performance parameters for this process, contributing to enhanced environmental protection.

For examining to what extent quartz in bauxite reacts with alkali solusion during the extraction of alumina, experiments have been made on the reaction of guartz in bauxite with caustic soda solusion and alumina pregnant liquor. The findings are as follows:1. The guantily of quartz dissolved in caustic soda solusion increases in proportion to the surface area of quartz. It increases also with the increase in the temperature and concentration of the sdusion. The dissolving velocity becomes about double per 10°C of temperatue-rising and about 1.3 times as alkali concentration is doubled.2. The reacting velocity of quartz in alumina pregnant liguor is slower than that in caustic soda solution. the velocity in alumina pregnant liguor with 1.7 of Na2O/Al2O3mol, ratio is 1/10 of that in caustic soda solution.3. It is presumed that the reacting quantity of quartz during the extraction of alumina from bauxite by low-pressure-Bayer-process using tri-hydrate bauxite is less than 2% of the contents of quartz in bauxite.

The direct synthetic method of polyglycerine (PG) by means of hydrolysis of epichlorohydrin (ECH) with caustic soda solution was investigated. The concentration of caustic soda solution considerably affected the yield and the molecular weight of PG. It was observed that the higher the concentration, the lower the yield and the higher the molecular weight. The glycerine content of PG was also affected by the concentration of the caustic soda solution, and the glycerine content increased with the decrease in the concentration.It was found, moreover, that water-soluble solid PG or insoluble and infusible PG, which was suggested to be cross-linked PG, was obtained when the hydrolysis of ECH was carried out with 30% caustic soda solution.When ECH and caustic soda solution were mixed in an autoclave and the hydrolysis was carried out under pressure, the reaction took place violently and no solid polymer was obtained. The product obtained was dark brown and unsaturated polymer, which was probably caused by the decomposition of some intermediates.Then, the method of desalting from PG was investigated. The electrodialysis was found the most effective method of desalting from PG. PG containing only about 1% salt was obtained from the PG solution containing about 15% salt. The loss of the organic substances, such as PG and glycerine, was only 7% in the process of the electrodialysis.

Investigations on the activation of cellulose by mixed solutions of caustic soda and urea are reported. The structural effects of those solutions on various dissolving pulps are studied by 13C‐CP/MAS‐NMR spectroscopy. In a series of steeping lyes, the concentration of NaOH was varied in a range from 0% to 8% and the urea‐concentration in a range from 15% to 40% at ambient temperature and −25 °C.Using solely the single NaOH or urea solutions in the concentration ranges given above, no or only minor structural changes were found. In contrast to that, the cellulose I structure was partially or completely destroyed by using the bicomponent solution with urea added to caustic soda. The structural effect of the bicomponent solutions is comparable with the effect of solely caustic soda solutions of approx. 10% to 18% NaOH. However, the 13C‐CP/MAS‐NMR‐spectra from the bicomponent pretreated samples indicate a structure different from the usual ordered structures of sodium cellulose I or II, namely a special urea‐NaOH‐cellulose complex. The results show that for cellulose activation the NaOH concentration of the caustic soda can be remarkably reduced by adding urea. The improved activating effect of an optimized caustic soda solution with added urea was proved to be useful for the synthesis of cellulose carbamate.

We studied the cyaniding of the roasted residues from Herrenshmidt Roaster and that of complex silver sulfides which belong to the stibnite group. The results of studies were as follows: 1) IIn, the straight cyaniding of roasted residues, the cyanide extraction of gold was about 74 per cent. and that of silver was only 32 per cent. 2) Artificial miargyrite ore destroyed much cyanide and extraction of silver was about 4 per cent.. The volatilized roasting for cyanide treatment was little effective. The roasted products having been treated with caustic soda solutions, the extraction of silver increased to 88 per cent. 3) The cyaniding of tetrahedrite silver ore and its roasted products was not satisfactory. As for the cyaniding of the roasted products, treated with caustic soda solutions, the higher the roasting temperatures, the less the cyanide extraction of silver became. It was found that tetrahedrite silver ore sintered at higher temperatures (above 900°) would not decompose by heat treatment with caustic soda solutions. 4) The roasted residues from Herrenshmidt Roaster having been treated with 8-10 per cent. caustic soda solutions at 80°-100° for 6-8 hours before starting cyanide treatment, the extraction of gold and silver increased remarkably. 5) Being treated with soda sulfide and sulfuric acid, antimony leached in the caustic soda solutions could be recovered as antimony trisulfide.

Crystallization of Al(OH)3 that occurs during the decomposition of caustic soda solutions is an important part of Bayer process for alumina production. Several phenomena, which influence the physicochemical characteristics of precipitated Al(OH)3, occur simultaneously during this process. They are nucleation, agglomeration, and crystal growth of Al(OH)3. In this article, we have investigated the mechanism of Al(OH)3 crystal growth from pure caustic soda solutions and in the presence of oxalic acid.The results have shown that the growth of Al(OH)3 crystals from caustic soda solutions follow the B + S model (birth and spread). New Al(OH)3 particles, formed during the decomposition process of pure caustic soda solutions, are characterized by regular hexagonal shape. The nuclei have the same geometry as the contact face. However, microstructural investigations of Al(OH)3 samples, obtained by crystallization from caustic soda solutions in the presence of oxalic acid, have shown the presence of nuclei of irregular shape in addition to regular ones. So, the presence of oxalic acid in the caustic soda solutions leads to a change in crystal habit.Besides, the results obtained by kinetic investigation confirmed the mentioned mechanism of Al(OH)3 crystal growth.

Recovery and purification of cresylic acids from FCC spent caustic soda solution were studied. By air-blowing, acidification, and distillation as described below, a fraction of cresylic acids having sweet odor was obtained, and its composition was examined.(1) Removal of mercaptanes by air-blowing in the presence or absence of a catalyst (such as 0.1wt% of tannic acid).Optimum results were obtained under the following conditions:pH of the spent caustic soda solution…10.8-11.4.Temperature…50°C.Air feed rate…60-80m3/hr./ton of the spent caustic soda solution.(2) AcidificationThen, the spent caustic soda solution treated with air was acidified to pH 10 with 40% sulfuric acid and the upper oily layer was separated. The oily layer was further acidified to pH 3 and crude cresylis acids in the upper layer were recovered.(3) DistillationThe crude cresylic acids obtained by the above procedures were then purified by distillation and divided into several fractions.Properties of the product:The cresylic acids thus obtained had sweet smell free from irritative odor of organic sulfur compounds. Total sulfur content of the product was small although the higher and lower fractions had somewhat higher sulfur content as compared with the intermediate fractions. Specific gravity and refractive index decreased with the rise of b. p. of the fraction, but they were higher in the residue. By infrared spectrum analysis of rectified cresylic acids, the distributions of o-, m- and p- cresols, xylenols, and phenol in several fractions were determined.

This problem concerns itself with the possibility of producing a reasonably pure concentrated caustic soda solution using trona as a starting material. It involves a carbonation process, purification of raw material and causticization with lime. Since soda ash costs a little less than three times what trona costs, the process has good commercial possibilities.

THE most striking property of the wool fibre is its ability always to return to its original length after stretching in cold water. If, however, a fibre is steamed in the strained position, it shows no tendency to return to its original length in cold water. So far as I am aware, it has hitherto been found impossible to induce such fibres to return to their original length, although partial recovery occurs on re-steaming in the absence of tension. During the course of another investigation, however, I have recently found that fibres which have taken a permanent set of the kind just described, recover the property of perfect elasticity in caustic soda solutions. For example, a fibre which had been stretched and steamed for 15 minutes at 47.4 per cent extension, returned to its original length in 14 minutes in 0.15 N caustic soda solution. Contraction does not cease when the original length is attained, but continues beyond this point until a real shrinkage of about 10 per cent of the original length is observed. The rate of recovery increases with the strength of the solution, but is measurable even in 0.01 N caustic soda. The discovery opens up a number of possibilities in regard to ‘finishing’ processes in the wool textile trade, but of even greater significance is the contribution which it makes to knowledge of the elastic phase in the wool fibre and the changes which it undergoes during stretching and steaming. Complete details of the results and conclusions of the investigation will be described in another place.

Conditions for electrolytic deposition of iron powder from a slurry of iron III oxide in caustic soda solutions were investigated. The variables that influence the deposition the most were temperature (90°C), caustic soda concentration (600–800 g/l), and low current densities. Results from pilot‐plant studies were in good agreement with laboratory findings. Several photomicrographs of the deposits are included. Physical and chemical properties of the powders are listed. Results show that a ductile, dendritic deposit was obtained that could be ground up easily. The size of the dendrites was influenced greatly by conditions of deposition. Particle size distribution, particle shape, ductility, flow rate, purity, and compactability of several powders were examined. Tensile strength and elongation of sintered compacts were also studied.

Integrated hydrometallurgical process for production of zinc from electric arc furnace dust in alkaline medium

In Europe, 50% of the production of the chemical industry depends on chlorine. Elf Atochem, the french leader in chlorine, has chosen to extend its chlorine capacity with the ion exchange membrane (IEM) process. The IEM have to be resistant to the aggressive electrolyte medium, have a very high permselectivity and conductivity. The chlor-alkali membranes are made of perfluorocarbon polymers with cationic exchange groups, sulfonic on the anodic side and carboxylic on the cathodic side. Their properties are well described by the cluster network model. The electrolyser and membrane evolution allow to obtain high caustic soda current efficiency (97%) and a voltage of about 3 V at 3 kA/m 2 , 90 o C and with a caustic soda concentration of about 35 wt %. Since 1990, a 50 wt % caustic soda solution can be produced directly in electrolysers using a new generation of multilayer ion exchange membrane. Despite the unfavorable economic climate in which the chlorine industry finds itself (overcapacity, environment), the IEM process has made a remarquable breakthrough: this technology appears to be the most economic and above all the most respectful of the environment. This process is already recognized as the substitute of the mercury process. Elf Atochem operates two chlor-alkali membrane plants: one of 80 kt Cl 2 /year in USA and a second of 120 kt Cl 2 /year in France