Effect of additives on crystal morphology in calcium oxalate crystallization process

Master thesis in the field of

Chemical Engineering

Kidney stones are one of the most common diseases in the world, most of its crystals are formed from calcium oxalate crystals. Therefore, it has been a long time that the investigation of effective substances in the control of this disease through the control of calcium oxalate crystals has been considered. The purpose of this research is to investigate the effect of tripotassium citrate on the structure and shape of calcium oxalate crystals as the main component of most kidney stones. In this research, the additive tripotassium citrate was used under different conditions in terms of temperature, concentration, mixing intensity, and pH using the Taguchi test design method and at three different levels in the form of the statistical design of the experiment and the L9 orthogonal array. The crystals formed from the crystallization process in each of the methods were filtered and dried. After that, the shape of the crystals was evaluated using SEM electron microscopic photography. The results of the statistical analysis And the microscopic photos indicate that tripotassium citrate has a significant and impressive effect on the morphology of calcium oxalate in the operating conditions: temperature of 25 degrees Celsius, concentration of 60 g/l, stirring speed of 150 rpm and pH equal to 8. Crystallization from solution is one of the most important operations that can produce products with the highest purity It is effective. In the pharmaceutical industry, the speed of dissolution is very important. Poor control over the shape and size of the produced crystals leads to unacceptable results in the next steps, such as the filtration and drying time. In the chemical fertilizer industry, growth morphology and particle size distribution are important because they determine product properties such as separation, fluidization, compaction, dissolution, and packaging. The products must be balanced during the storage period and have the ability to dissolve properly to be absorbed by the soil and plants. In the pharmaceutical industry, this issue becomes more sensitive (Sangwal, 2007). In an optimal crystallization, the product has a smooth surface and high purity, and the size of the particles is also determined according to its application. Morphology and characteristics related to the shape of the crystal are also important in the investigation of kidney stone disease. The purpose of this research is to study the effect of additives on the shape of calcium oxalate crystals as the most common type of kidney stones. The monohydrate type of this crystal is the most abundant form of calcium oxalate kidney stones due to its high thermodynamic stability. This species has a hexagonal shape and a sharp edge that cannot be discarded and has the ability to grow. An attempt is made to change its shape to a round and edgeless double-breasted form, an effective step is taken to reduce the formation of this stone and dispose of it as easily as possible. It creates salts and other substances in the blood. In the definition of kidney stone, it can be said that a kidney stone is a hard object that is formed by crystals that grow in the urine. Kidney is one of the internal organs of the human body and some other living beings. The kidney acts as a filter for blood purification and produces urine. Inside each kidney, there are more than a million functional units called nephrons [1]. Each nephron consists of a very small filter called clofa [2] which is connected to a small tube. Water and waste materials are separated from the blood by this filter and flow into small tubes. Most of this water is reabsorbed by small tubes, and waste materials enter the urine in a concentrated form to be excreted. The urine collected from the small tubes enters the funnel-shaped part called the renal pelvis and then enters the bladder through a tube called the urethra (Wikipedia).

1-3- Kidney stone disease

Although the kidneys are small organs, they are responsible for many vital tasks, including purifying waste materials and excess fluids from the blood, which is effective in maintaining the general health of the body. Severe kidney disease may lead to its complete failure, which requires treatment with dialysis or a kidney transplant to prevent death.

Kidney stone disease has become one of the most common diseases in the last century.. There are different types of kidney stones and they are composed of organic and inorganic materials. Inorganic compounds are the most important component of them, which make up almost 98% of the weight of stones. Calcium stones such as calcium oxalate and calcium phosphate are among the most common stones that are deposited in the kidney, and more than 70 to 80% of them are composed of calcium oxalate (Khan, 1993).

Figure 1-1 shows examples of calcium stones. Also, Figure 2-1 shows examples of stones in the kidney. If the body's self-control system is not able to prevent the formation of stones or remove the produced stones, other methods should be used to treat this disease. Patients with kidney stones are treated by various ways such as surgery, use of oral supplements and use of herbal medicines. In recent years, due to the increase in public awareness about the complications of kidney surgeries, drug treatment has increased significantly. Table 1-1 shows the types of kidney stones and the percentage of their formation.

[1]- Nephron

[2]- Glomeruli

-4- Investigation of the production of kidney stones

The amount of ions or molecules dissolved in a solution is determined by a parameter called the concentration product[1] (CP) which is equal to the product of the concentration of the pure chemical components of the salt. is For example, CP of sodium chloride salt is equal to CP = [Na+][Cl-]. If the aqueous solution of a salt reaches the point where no salt crystals are dissolved in it, it is called a saturated solution. In this case, CP is called thermodynamic solubility product [2] (Ksp). In urine, although the CP of calcium oxalate exceeds the thermodynamic product, crystallization does not occur due to the presence of natural inhibitory substances.

When the stone-forming salts in the urine reach a supersaturated state, the salts are not able to remain in solution in the urine, so the molecules or ions dissolved in the urine are precipitated and the first nuclei of kidney stones are produced. At this point, CP is called the product of crystal formation [3] (Kf). The product of thermodynamic solubility and the product of the formation of three major saturation regions are distinguished from each other: the sub-saturation region [4], the quasi-stable region [5] and the unstable region [6]. In the sub-saturation region, crystals are not formed under any conditions, and if there is a crystal in the solution, it dissolves. Crystals usually do not form spontaneously in the quasi-stable region. In this area, there is no possibility of nucleation and production of new crystals during the period when urine is filtered in the kidney, but under certain conditions, nucleation may also occur in this area. For example, due to the presence of obstruction in some points of the kidney, the passage time of urine may be long enough to create nucleation, so there is a possibility of nucleation of crystals in these points.

[6]- Unstable

ABSTRACT

Effect of Additives on Crystal Morphology in a Crystallization Process of Oxalate Calcium

Major part of Kidney stones, the most common diseases in the world, are formed by calcium oxalate. Recently, investigation of effective factors in controlling the kidney stone diseases through the controlling of oxalate calcium crystals was noticed. The aim of this study was to investigate the effects of tripotassium citrate on the structure and shape of calcium oxalate crystal as the main component of most kidney stones. In this study additive materials were used to affect the four different factors temperature, concentration, rate of mixing, and pH by Taguchi experiment design method at three different levels in the design of statistical experiment and orthogonal array L9( ). Crystals formed in the crystallization process of each test were filtered and dried. Subsequently, the crystals were evaluated using electron microscopy images (SEM).