Disc Granulation Process of Carbonation Lime Mud as a Method of Post-Production Waste Management

: Carbonation lime mud is a by-product formed during the production of sugar in the process of raw beetroot juice puriﬁcation. On average, during one campaign, over 12,000 tons of carbonation lime mud is obtained in the operation of one sugar production plant. It is stored in prisms, which negatively a ﬀ ects the environment. The chemical properties of carbonation lime mud allow using it as a soil improver. This article presents the results of research into the development of carbonation lime mud disposal technology and its management. The chemical composition and physical properties of waste were determined. It has been proposed to use carbonation lime mud as the basic raw material in the production of mineral–organic fertilizers. Tests were conducted in a disc granulator. The granulated material was wetted with water and aqueous solution of molasses. Carbonation lime mud is a material that is easily subjected to the granulation process, using any wetting liquid. The beds wetted with 33% and 66% solutions of molasses are characterized by a greater homogeneity and smaller size of the obtained product. During experiments in which wetting with water was applied, the product obtained after drying demonstrated low resistance to compression; granules wetted with 33% aqueous solution of molasses demonstrated resistance to compression below 10 N; and granules wetted with 66% aqueous solution of molasses demonstrated resistance to compression above 10 N.


Introduction
Carbonation lime mud-also called defecosaturation mud-is the by-product formed during the production of sugar in the process of raw beet juice purification.
The process of defecation occurs during liming and saturation of the solution of sucrose with carbon dioxide. In the presence of calcium, gelatinous complexes of calcium saccharate-carbonate are then formed in the form of poorly soluble gels. During saturation, the precipitation of calcium carbonate occurs. It is absorbed by colloidal impurities (non-sugars). During this process, the precipitation of insoluble calcium salts, organic acids, and non-organic pectic substances, and their passage to the deposit occurs. The main component of carbonation lime mud is CaCO 3 , whose share reaches up to 50% [1].
On average, in the operation of one sugar production plant during one campaign, over 12,000 tons of waste carbonation lime mud. It is stored in prisms, which negatively affects the environment.

Property Value
Range of changes in grain size (mm) 0-0.56 Average grain size (mm) 0.12 Tangent of the angle of natural repose 1.34 Bulk density (kg/m 3) 1131 Humidity 38% In addition, elemental composition occurring in the raw material was examined. The content of separate elements was analyzed using atomic absorption spectroscopy (AAS). The determination was performed in accordance with PN- ISO-8288:2002. A sample weighing about 100 mg was wet mineralized in the closed system in an Anton Paar Multiwave 3000 V 2.02 microwave extractor. An examination procedure, the so-called blank test, was performed for each series of mineralization. The mineralization of each sample was performed in two repeats. The concentration of metals was determined using atomic absorption spectroscopy (AAS) and electrothermal atomic absorption spectroscopy (ET-AAS) on a Perkin-Elmer 3110 spectrometer equipped with a graphite tray of the HGA 600 type (USA). The chemical composition of carbonation lime mud obtained as a result of the above tests is presented in Table 2. , and additionally, this mud is rich in elements typical of mineral fertilizers commonly used in the agricultural sector.
Despite the beneficial chemical composition, the practical qualities of the material need to be modified-in particular, its granulometric composition-in order to eliminate dusting and agglomeration. They are unfavorable phenomena occurring during transport, storing, and dosing fertilizers to soil. To eliminate the mentioned usability faults, the fertilizer's granulometric composition was initially determined at 1-10 mm. This corresponds to the commercial characteristics of other agricultural fertilizers. After initial tests, the optimum size fraction of 2-6 mm was assumed. The value of force applied to fertilizer's granules without destroying their structure, for the assumed size, should be no less than 10 N.

Testing Properties and Chemical Composition of Carbonation Lime Mud
The main part of the granulator is a rotating disc with a diameter d = 0.5 m and height of the rim h = 0.08 m. The granulator disc is mounted to a shaft and connected to the electric motor by means of belt transmission and a regulator. The rotational speed is determined and controlled by means of an inverter. Wetting liquid is provided from the container mounted at the height of 2.5 m through a hydraulic sprinkler, and its flow intensity is measured by a rotameter.
Carbonation lime mud obtained from waste dumps, due to high initial humidity and the phenomenon of agglomerating, required initial screening. The material was screened on sieves with a mesh size of 1 mm. The granulation process was conducted in the disc granulator Figures 1 and 2 in a periodic way. Each time 1 kg of screened material (carbonation lime mud or the mixture of mud and gypsum) was placed on the disc, then the disc was set in rotational motion so that the material circulated freely inside the disc rotating at the speed of 9.5 rpm. Directly after the commencement of the process, the material was wetted with wetting liquid. At first, water was used for wetting, while in the next trials, solutions of molasses with concentrations of 33% and 66% were applied as well. The material was wetted by the droplet method in the case of trials to which water was added or by continuous stream when an aqueous solution of molasses was added. The wetting time t n was changed within the range 4-8 min. During wetting, about 200 mL of liquid was provided to the bed each time. This liquid was necessary to initiate the formation of granules. Due to the high initial humidity of the material and over-wetting of the bed at the end of the process necessary in the case of such a specific raw material, the formed granules were powdered by various loose materials, the use of which prevented the agglomeration of granules. Moreover, the additional benefit was that the mineral components contained in the powder improved the quality of the final product (fertilizer) and improved its diversity. Raw materials commonly used in the fertilizer industry-that is, dolomite, chalk, limestone flour, and gypsum-were used as powder. In addition, trials in which no powder was applied and when the over-wetted bed was powdered with carbonation lime mud were performed. In the case of trials with powdering, the total process time t g depending on the type of liquid used for wetting changed within the range 6-30 min. Granulation was run until the majority of the fine-grained material attached to granules, making sure that the agglomeration of granules did not occur (no coalescence phenomenon), which would cause the excessive increase in the size of formed agglomerates.
After the completion of granulation, the obtained product was weighed and then dried at temperature 96 • C for 24 h. After the drying process, the granules in Figure 3 were weighed again, and then measurements of the particle size distribution, humidity, angle of natural repose, and bulk density of the product were conducted, and the resistance to the compression of selected size fractions was determined. The granulated product was screened using sieves with mesh sizes: 12.5; 10.0; 8.0; 6.3; 5.0; 4.0; 3.0; 2.0; and 1.0 mm, which enabled the determination of the mass share of separate fractions in the obtained granulate. Table 3 presents parameters of the conducted trials of carbonation lime mud granulation. and improved its diversity. Raw materials commonly used in the fertilizer industry-that is, dolomite, chalk, limestone flour, and gypsum-were used as powder. In addition, trials in which no powder was applied and when the over-wetted bed was powdered with carbonation lime mud were performed. In the case of trials with powdering, the total process time tg depending on the type of liquid used for wetting changed within the range 6-30 min. Granulation was run until the majority of the fine-grained material attached to granules, making sure that the agglomeration of granules did not occur (no coalescence phenomenon), which would cause the excessive increase in the size of formed agglomerates.  After the completion of granulation, the obtained product was weighed and then dried at temperature 96 °C for 24 hours. After the drying process, the granules in Figure 3 were weighed again, and then measurements of the particle size distribution, humidity, angle of natural repose, and bulk density of the product were conducted, and the resistance to the compression of selected size fractions was determined. The granulated product was screened using sieves with mesh sizes: 12.5; 10.0; 8.0; 6.3; 5.0; 4.0; 3.0; 2.0; and 1.0 mm, which enabled the determination of the mass share of separate fractions in the obtained granulate. Table 3 presents parameters of the conducted trials of carbonation lime mud granulation.  After the completion of granulation, the obtained product was weighed and then dried at temperature 96 °C for 24 hours. After the drying process, the granules in Figure 3 were weighed again, and then measurements of the particle size distribution, humidity, angle of natural repose, and bulk density of the product were conducted, and the resistance to the compression of selected size fractions was determined. The granulated product was screened using sieves with mesh sizes: 12.5; 10.0; 8.0; 6.3; 5.0; 4.0; 3.0; 2.0; and 1.0 mm, which enabled the determination of the mass share of separate fractions in the obtained granulate. Table 3 presents parameters of the conducted trials of carbonation lime mud granulation.      The presented results concern trials of carbonation lime mud granulation in which water, 33% solution of molasses, and 66% solution of molasses were applied as wetting liquid. In all trials, whose results are compared in Figures 4 and 5, the final powdering of the over-wetted granulate by means of fine-grained limestone flour ( Figure 4) and dolomite ( Figure 5) was applied.  The presented results concern trials of carbonation lime mud granulation in which water, 33% solution of molasses, and 66% solution of molasses were applied as wetting liquid. In all trials, whose results are compared in Figures 4 and 5, the final powdering of the over-wetted granulate by means of fine-grained limestone flour ( Figure 4) and dolomite ( Figure 5) was applied.  The presented results concern trials of carbonation lime mud granulation in which water, 33% solution of molasses, and 66% solution of molasses were applied as wetting liquid. In all trials, whose results are compared in Figures 4 and 5, the final powdering of the over-wetted granulate by means of fine-grained limestone flour ( Figure 4) and dolomite ( Figure 5) was applied.

Results and Discussion
The analysis of the obtained results indicates that the most beneficial sizes of granulated fertilizer are obtained during trials with wetting the bed with 66% aqueous solution of molasses.
The product obtained for these trials is characterized by granulometric composition with particles slightly smaller than during wetting with water and 33% solution of molasses, which is more beneficial during dosing fertilizer to soil. During trials with 66% solution, more than 99.5% of the material mass was granulated, which indicates on one hand better process conditions and on the other the less wear of agglomerates formed earlier. The product's resistance to wear is of major importance during transport, when fertilizer granules slightly change their mutual location, causing friction between their external surfaces. A parameter that is characteristic of the strength properties of the obtained granulate is its compressive strength. This property is very important during storing fertilizer in bags or 1-ton packages, in which it presses on granules that are at the bottom of the package. Initial experiments demonstrated that granules obtained during wetting with water break down under small load; therefore, tests of resistance to compression were conducted only for trials performed during the wetting with solutions of molasses.
The analysis concerning the value of compressive force at which the destruction of granules occurred was conducted for agglomerates with sizes of 4, 5, 6.3, 8, and 10 mm. Tests were conducted on the Instron analyzer- Figure 6, which measured the value of force in the function of the displacement of a head that compressed a granule. The maximum value of destructive force is illustrated in graphs by the local minima of the presented graphic dependencies in relation to the initial value. Each time the resistance of five granules from each size class was examined, and then the arithmetic mean was calculated. The exemplary results of measurements of resistance to compression for granules obtained during granulation with wetting with solutions of molasses are presented in Sections 3 and 3. Graphic dependencies present the value of compressive force at which the breaking down of the examined granule occurs (minimum in the graph). In each figure, the results of compression for five randomly selected granules from a given size fraction are presented. The negative value in the graph for the compressive load results from the assumption adopted by the calculation program in which tension forces are defined as positive and compressive forces are defined as negative. Figure ?? presents exemplary results of strength tests conducted for granules with sizes 4-5 mm, concerning trials in which gypsum was used for powdering over-wetted agglomerates. It can be seen on their basis that the sufficient resistance of granules to compression (about 20 N) is obtained during granulation with the use of 66% solution of molasses. Analogous results (Figure ??) were obtained for granulates powdered with dolomite. It can be assumed that resistance to compressive force is more affected by the concentration of the used solution than by the type of material used for powdering the granulated bed.     The results of tests concerning the strength of granules Table 4 confirm that granulate obtained during wetting with 66% aqueous solution of molasses meets the strength requirements. However, the technology of disc granulation of carbonation lime mud requires further optimization, which on one hand would concern obtaining desired results with using solutions with less concentration of molasses-lower production costs-and on the other, expanding the commercial offer concerning the final product. The results of tests concerning the strength of granules Table 4 confirm that granulate obtained during wetting with 66% aqueous solution of molasses meets the strength requirements. However, the technology of disc granulation of carbonation lime mud requires further optimization, which on one hand would concern obtaining desired results with using solutions with less concentration of molasses-lower production costs-and on the other, expanding the commercial offer concerning the final product.

Conclusions
Carbonation lime mud granulation is a beneficial technology of post-production waste management. Carbonation lime mud due to the content of lime in its composition and due to the low level of heavy metals' concentration is a promising raw material in the production of agricultural fertilizers.
Mud granulation enables obtaining mineral-organic fertilizer with the desired mechanical properties and beneficial chemical composition, meeting the commercial requirements. The proposed granulation technology expanded by the stage of powdering enables enriching fertilizer with other mineral components. Carbonation lime mud is a material that is easily subjected to granulation with the use of any wetting liquid. The bed wetted with 33% and 66% solutions of molasses is characterized by the greater homogeneity and smaller size of the obtained product.
Based on the conducted strength trials, it can be concluded that during experiments in which wetting with water was applied, the product obtained after drying demonstrated low resistance to compression; granules wetted with 33% aqueous solution of molasses demonstrated resistance to compression below 10 N; and granules wetted with 66% aqueous solution of molasses demonstrated resistance to compression above 10 N. Granulation changes the starting material with a grain size of 0-0.5 mm (with a predominance of fine fractions) into a bed with agglomerate sizes in the vast majority above 1 mm. Due to the fact that this waste (mud) is stored in heaps, dusting occurs on windy and dry days of the tiniest fractions. After granulating, such material, due to its chemical composition and the use of additives, can be a soil de-acidifying fertilizer-it can be sold. Molasses solution (also waste) is successfully used as a binding liquid. So, instead of ecological problems with dusty waste, you can generate profits from the sale of fertilizer, the basic components of which are sugar waste. In addition, in one of the variants, sulfogypsum is also used as an additive-which is also waste from flue gas desulfurization. The idea is dedicated to sugar factories that can buy a "know how" and start producing fertilizer instead of paying environmental fees and fines.