Lime-soda Process Research Articles

Removal of total hardness using low cost adsorbents

Water hardness is an undesirable quality of water in many regions around the world. Hardness can be removed by different methods like ion exchange method, reverse osmosis, distillation, lime soda process etc. But owing to the increase in cost, energy and hectic processes in these methods, it is essential to find an alternative method for softening of water. Nowadays, adsorption methods are gaining attention due its simplicity and efficiency. Efficiency of different adsorbents like Amorphophallus campanulatus (Elephant foot yam), wheat straw ash and rice husk ash and coconut shell activated carbon which are naturally available are investigated in this study. Yam is freely abundant and found to be more efficient compared to others. The efficiency of softening is above 80% for yam. Value of equilibrium constant (RL) and adsorption intensity factor (n) gives the feasibility and intensity of adsorption. Acidic modification has given a negative impact in softening of water for the used materials. High carbon containing substance in ash form has brilliant adsorption ability. Investigations to find out efficiencies are done by optimizing parameters such as adsorbent dosage, pH and contact time. The performances are assessed by isotherm studies. These studies and experiments are done to suggest a simple setup which rectifies the problems of conventional methods for the removal of hardness.

An Electrochemical Cell for Selective Lithium Capture from Seawater.

Lithium (Li) is a core element of Li-ion batteries (LIBs). Recent developments in mobile electronics such as smartphones and tablet PCs as well as advent of large-scale LIB applications including electrical vehicles and grid-level energy storage systems have led to an increase in demand for LIBs, giving rise to a concern on the availability and market price of Li resources. However, the current Lime-Soda process that is responsible for greater than 80% of worldwide Li resource supply is applicable only in certain regions on earth where the Li concentrations are sufficiently high (salt lakes or salt pans). Moreover, not only is the process time-consuming (12-18 months), but post-treatments are also required for the purification of Li. Here, we have devised a location-independent electrochemical system for Li capture, which can operate within a short time period (a few hours to days). By engaging olivine LiFePO4 active electrode that improves interfacial properties via polydopamine coating, the electrochemical cell achieves 4330 times amplification in Li/Na ion selectivity (Li/Na molar ratio of initial solution = 0.01 and Li/Na molar ratio of final electrode = 43.3). In addition, the electrochemical system engages an I(-)/I3(-) redox couple in the other electrode for balancing of the redox states on both electrode sides and sustainable operations of the entire cell. Based on the electrochemical results, key material and interfacial properties that affect the selectivity in Li capture are identified.

Use of Carbonatites in the Production of Precipitated Calcium Carbonate: A Case Study from Eppawala, Sri Lanka

The study investigates the possibility of using carbonatite in the production of precipitated calcium carbonate (PCC). We made use of fresh apatite-rich carbonatites found at the phosphate mining sites at Eppawala, Sri Lanka. Analyses of the fresh carbonatite were performed with the aid of optical microscopy, powder X-ray diffraction (XRD), atomic absorption spectrophotometry (AAS), UV/visible spectrophotometry (UVVS), and thermo gravimetric analysis (TGA). Quicklime obtained from calcinations of carbonatites was used in synthesizing PCC via a lime-soda process. The end product was analyzed with XRD, TGA, AAS, and UVVS. Results revealed that the most common CO3 2− phase available in fresh carbonatites is calcite (>65%). The Ca-rich CO3 2− phase can be distinguished easily from other available minerals because its mode of occurrence in carbonatite matrix is different to that of other minerals. The results of TGA show that the decomposition of CO3 2− phase initiates at about 340°C, which leads to lower energy consumption during calcinations. Post-magmatic hydrothermal process may have been the cause of the formation of thermally unstable CO3 2− phases. Hydration of quicklime from the carbonatite yields much higher Ca2+ in the solution than from marble under the same experimental conditions. The synthesized PCC particles are in the calcite polymorphic form. The purity of PCC varies from 96 to 98 wt%. The maximum precipitable CaCO3 from 1 g of quicklime is about 1.1 g. Hence, fresh carbonatites has great economic potential for the production of PCC.

Byproduct Recovery from Reclaimed Water Reverse Osmosis Concentrate Using Lime and Soda‐Ash Treatment

Lime and soda-ash softening of reclaimed water reverse osmosis concentrates as a pretreatment step for concentration by seawater reverse osmosis was the focus of this study. The objectives were removal of the potential fouling minerals of calcium, magnesium, and silica by selective precipitation, while producing byproducts with potential resale value. Three different bench-scale lime-soda processes were evaluated. The traditional method produced low-quality magnesium hydroxide [Mg(OH)2] and calcium carbonate (CaCO3) byproducts. A modified process with pre-acidification to eliminate carbonate removed 98 to 99% of calcium and magnesium and produced CaCO3 that was > 94% pure. To prevent the contamination of byproducts with calcium sulfate (CaSO4) in high-sulfate concentrates, a CaSO4 crystallization step was added successfully to the modified process to precipitate CaSO4 before Mg(OH)2 precipitation and produce gypsum that was 92% pure. The modified lime-soda process also removed 94 to 97% silica, 72 to 77% barium, and 95 to 96% strontium, which are known as reverse osmosis membrane foulants.

Effect of Hydraulic Activity on Crystallization of Precipitated Calcium Carbonate (PCC) for Eco-Friendly Paper

Wt% of aragonite, a CaCO3 polymorph, increased with higher hydraulic activity (°C) of limestone in precipitated calcium carbonate (PCC) from the lime-soda process (Ca(OH)2-NaOH-Na2CO3). Only calcite, the most stable polymorph, was crystallized at hydraulic activity under 10 °C, whereas aragonite also started to crystallize over 10 °C. The crystallization of PCC is more dependent on the hydraulic activity of limestone than CaO content, a factor commonly used to classify limestone ores according to quality. The results could be effectively applied to the determination of polymorphs in synthetic PCC for eco-friendly paper manufacture.

Laboratory Scale Production of Commercial Grade Calcium Carbonate from Lime-Soda Process

Quality precipitated calcium carbonate has much demand in various chemical and allied industries as filler, surface coating, whitening, adhesive etc. A study was carried out by modifying classical lime-soda process to obtain high quality precipitated calcium carbonate. The experiments were carried out in two stages using commercial and analytical grades of sodium carbonate and lime as reactants. After causticization, the filtrates from the washing of calcium carbonate were used to prepare all solutions for reactions in next stage. The precipitated calcium carbonate obtained from the process was analyzed and comparisons were made with the commercially available precipitated calcium carbonate produced from carbonation method. The calcium carbonate produced from causticization was superior to those produced by carbonation method in the country. The crystal structure of carbonate was calcite.Keywords: Causticization; Settle Volume; Bulk Density; Yield.DOI = 10.3329/cerb.v12i0.1490 Chemical Engineering Research Bulletin 12 (2008) 1-6

Chemical Treatment of Leached Residue from Manufacture of Sodium Chromate in the Lime-Soda Process

A process for converting the leached residue into useful materials was investigated (Fig.1). When nitric acid was added in slightly less than stoichiometric amount required to combine with constituents except Fe2O2- in the residue, a good separation of Fe2O3 and SiO2- from other constituents was obtained (Table 2), and a gelatinous precipitate containing mainly MgO, Al2O2- and Cr2O2- was obtained by the reaction of the filtrate with slaked lime (Table 3). Zeolite (species P) was obtained from this gel by the addition of SiO2 and NaOH.Sulfuric acid was added to the remaining calcium nitrate solution to recover nitric acid, and crystal growth of calcium sulfate dihydrate in the nitric acid solution was also studied.

The Thermosludge Water Treating and Steam Generation Process

Abstract The Thermosludge process internally softens and makes high-pressure steam directly from hard and saline oilfield or other water. Pilot plant and early full-scale plant work established several physical and chemical principles found necessary or desirable for good operation, and for control and practical elimination of scale on the process heating surfaces. These principles are use of a secondary liquid heat transfer medium, provision of time and space for water chemical reactions ahead of the boiling zone, and presence of sludged reaction products throughout the boiling zone. Other pertinent factors are discussed such as dissolved and suspended solids limits, foaming, corrosion, and heat transfer. Introduction In 1964 considerable use of steam in California oil fields was beginning to cause shortages of good steam generator feedwater in some areas. It seemed evident that in some situations oilfield brine or other low-quality water would have to be used to generate high-pressure steam directly. The Thermosludge process was developed to meet this need, and early results of its field use have been reported previously. This article discusses both pilot plant and full-scale plant design and operation particularly relative to the high-temperature reactions and scaling characteristics of some of the chemicals present in the waters. Present understanding of the process should allow broader use in its original field, and in other processing areas dealing with difficult waters. Pilot Plant Design and Operation After considerable study of chemical and engineering factors involved, a pilot plant program was set up. Three main theories or principles believed to lead to successful operation were followed in the pilot plant design and the same principles were carried into the full-scale plant design. First, heat should be applied via a secondary fluid heat transfer medium rather than directly in a combustion space. Relative to direct-fired beating, the secondary fluid heating guarantees that maximum tube wall temperature will be well within the allowable metal temperature limit regardless of local scaling or salting up. Many situations call for soluble salt in the steam generator in concentrations of as much as 15 percent by weight perhaps half of the limiting solubility. Even if conventional tube scaling were somehow entirely prevented, such situations would require the inherent heat flux control of a secondary heat medium to prevent gross fouling and plugging by salt deposits. Second, means should be provided in terms of high-temperature time and volume to preheat and chemically react the feedwater before it enters the boiling zone. The practicality of this is based on the expectation that thermally induced mineral sludging reactions will proceed much faster and more completely in the 350 to 600F environment than, for example, in the conventional lime-soda process. Thus, the feedwater should be entirely softened by the time it arrives at the boiling zone.

Design Aspects of Lompoc Water Treatment Plant

Ground water with 750 mg per 1 total hardness and 1,300 mg per 1 total dissolved solids is being successfully softened and filtered at Lompoc, California’s new municipal water treatment plant using the cold lime-soda process followed by recarbonation. An automatic diatomaceous earth filtration system using vacuum type diatomite filters is used instead of rapid sand filters.

Upflow Solids Contact Basin

Principles of separation of solids from water by addition of chemicals are explained; as example, basin of Bacchus Marsh, Australia for lime-soda process is given; feature of basin is new slurry weir, for transferring old solids from top of slurry pool to concentrator at same rate as new ones are formed at bottom of slurry pool; calculations on quantity and concentration of slurry and resulting dimensional requirements; method of decanting supernatant liquor.

New Laboratory Data Relative to Embrittlement in Steam Boilers

Abstract Results of laboratory tests show that purified sodium hydroxide will not produce cracking of steel test specimens in short-time tests, whereas technical sodium hydroxide made by the lime-soda process will produce cracking. When the impurities present in the technical sodium hydroxide are added to the purified caustic and then used in tests, the specimens crack. It appears that when silica is present in sufficient amounts along with the pure caustic, cracking will take place. However, when smaller amounts of silica and small amounts of calcium, magnesium, and aluminum are added to the pure caustic, cracking will also take place. These results indicate that it is apparently necessary to have one or more catalysts present in the sodium-hydroxide solution in order to cause cracking within a reasonable period of time.

Softening Municipal Water Supplies by Zeolite

There is a widespread and increasing interest in the subject of the softening of hard municipal supplies. Now that the majority of the larger communities have purified their water it may be expected that more attention will be given to obtaining a softer product. The lime-soda process has been generally employed by most municipalities which have softened their water. With the rediscovered effectiveness of carbon-dioxide in the prevention of afterdeposits of lime in filter sands and in pipe lines, this method has had a considerable impetus in the last few years. Although the merits of zeolites as softening agents have been recognized for many years in connection with commercial and domestic plants, little use of that product has been made in reducing the hardness of municipal supplies. Actual information concerning the operating results of municipal softening plants employing zeolites has been comparatively meager. It is with the purpose of contributing to the literature on this phase of the subject that this paper is written. The general term is applied to a group of products, some synthetic and some natural, consisting of combinations of iron, aluminum, and sodium largely in silicate form. They have the quality in common, that hard water on being passed through a bed of zeolite sand exchanges its calcium and magnesium for the sodium in the zeolite until the sodium reaches exhaustion. On the introduction of a brine solution into the zeolite bed, the ionic reaction is reversed, the magnesium and calcium (as chlorides) being rinsed out of the bed to waste and the sodium remaining in the zeolite, making it ready for another softening cycle. About four years ago the Ohio Valley Water Company authorized its engineers to report upon a plant for softening the water supplied by that company to a suburban population of 60,000 people on the Ohio River just below Pittsburgh, Pa. The water delivered averaged

Water Softening Plant and Pumping Station Improvements at Fostoria, Ohio

Just as there are trends in industry, in the stock market, in education, in sewage disposal practice and in many other activities of the human race so there is a trend in the water works field, namely, to supply soft water. It is not an easy matter for municipally owned plants to proceed to furnish a soft water supply, whether naturally or artificially softened, due to the very nature of our government, but the many softening plants now in use or in the projected state attest to the success of water works engineers not only in the design of softening works but in establishing the economics of a soft water supply for industrial use and domestic consumption. Greenville, Ohio; Jefferson City, Mo.; the Ohio Valley Water Company (supplies Bellevue, Ben Avon, McKees Rocks, West View and others in the Pittsburgh district); Apollo, Pa. and Wheeling, W. Va., of recent design by the writer's firm are now in operation. The Fostoria plant will be operating, it is hoped, by this time next year. The Sewickley, Pa., softening plant is now in the course of design and softening plants are being considered by other clients. Other engineers record like progress in the design and installation of softening plants. Softening as employed in public water supplies generally assumes one of two types the lime-soda process or the zeolite method, the type used depending upon local conditions. Of the above named plants, that of the Ohio Valley Water Company is a zeolite plant capable of softening 4 million gallons daily to zero hardness. This plant is the largest of this type so far built for softening a public water supply. For Sewickley, Pa., studies have been completed on a marked variation of one of the above named types. The Fostoria softening plant is of the lime-soda type, the feature of which will be the combination of the functions of clarifier and settling basins in one unit and the, provision for recirculation of clarifier sludge as an enhancement in the softening process.

The Relative Merits of Lime‐Soda and Zeolite Water Softening

Water softening is fast coming into such general practice that every waterworks man is being brought more and more in contact with the subject. Whether in an operating or consulting capacity, he frequently must make decisions or recommendations as to the most advantageous method of treatment and the most suitable equipment. The purpose of this brief paper, written by a member of an organization which manufactures both lime-soda and zeolite water softeners, is to point out that neither process is to be recommended indiscriminately. Each has its advantages and each its limitations. Each has, therefore, its particular fields of usefulness, although, in a few cases, the choice is a debatable question. The principal reason for the particular applicability of either method lies in the nature and chemistry of the processes themselves. In the lime-soda process enough lime and soda are added to the raw water to remove the calcium as calcium carbonate, and the magnesium as magnesium hydrate. In the zeolite, or base exchange process, the calcium and magnesium in the various compounds in the raw water are replaced by sodium from the zeolite, so that the softened water contains the slightly greater equivalent weights of the sodium compounds. When the zeolite has given up all of its replaceable sodium, the supply is renewed by regenerating the zeolite with a solution of common salt. As far as hardness is concerned, the lime-soda process, as ordinarily practiced in the cold, yields a water with a residual hardness of 3 to 5 grains per gallon of calcium carbonate equivalent. The same process, carried on at or near the boiling temperature, may be made to deliver a water with a hardness of 1 to 3 grains per gallon. With the zeolite process, water may be softened to zero hardness.