## 1 Introduction  
Every day we encounter various agricultural and industrial products for our easiness and requirements. Out of these products, various products have different origin and chemical values. Agricultural industries is the backbone of any country, due to its importance in any countries GDP [1; 2]. In addition, there are several other industries like steel, mineral processing, paper, and pulp industries etc., which also play a major role in a human's life. Both these types of industries fulfills our daily requirements. The progress of any country is measured by the growth of their industries. However, one major drawback with such industries is that they produces million tonnes of by-products every day throughout the whole world [3]. The accumulation of byproducts from such industries leads to the various forms of pollution due to the presence of toxic constituents [4]. The agricultural industry waste like citrus peel waste, paper and pulp waste contain moisture and attracts the flies and bugs leading to the health related issues [5]. While, the industrial waste like fly ash by-products of thermal power plants [6], gypsum waste from medical and hospitals leads [7] to the accumulation of hazardous by products due to the presence of heavy metals, etc. Here, we have focused on the recycling of calcium rich agricultural and industrial waste for the synthesis of value added minerals like calcium carbonate and calcium oxide. Both of these minerals are biocompatible, non-toxic, and used every day in oils, plastic, imaging purposes, alloys and catalyst [8], environment-friendly items [9], calcium-enriched food [10; 11], drug delivery [12; 13], cosmetics and pharmaceuticals [10], templates for microcapsules [14; 15], and bone filling material [12]. Currently the commercial production of CaCO\({}_{3}\) calcium oxide and other derivatives of calcium is mainly carried out by using quick lime as a precursor material. Most of these quick limes are obtained by the mining which is laborious, and energy intensive process hence the final product is comparatively expensive [16]. So, there is an immediate need of a sustainable, economical, and an alternative source of calcium rich materials. There are several materials in our environment which are rich source of CaCO\({}_{3}\) like limestone, marbles, gypsum waste, cockle shell, eggshell, incense sticks, and high calcium fly ash (class C) and hard shell of shellfish, i.e., marine organisms (snails, oysters, shrimps, and pearls) [17; 18; 19]. Calcium carbonate (CaCO\({}_{3}\)) is a white color powder and water insoluble-inorganic biomaterials [18]. In nature, CaCO\({}_{3}\) is present in three different forms, i.e., calcite, aragonite, and vaterite [20]. Due to its biocompatible nature, aragonite receives extensive research attention worldwide. Among all these three polymorphs, calcite is thermodynamically most stable [21]. Calcite is the most stable polymorph of CaCO\({}_{3}\)[22], but aragonite has higher density and hardness from the other two polymorphs of calcium carbonate, which makes them very suitable material in plastic, paper, glass, fiber, and other industry [23]. A study reported the needle-shaped aragonite synthesis under a controlled injection of CO\({}_{2}\) in Ca(OH)\({}_{2}\) slurry suspended MgCl\({}_{2}\) aqueous solution. These investigators also reported that the residual MgCl\({}_{2}\) solution from the previous step, could be reused for the synthesis of aragonite synthesis as both Mg\({}^{2+}\) and Ca\({}^{2+}\) ions are not incorporated into the aragonite crystals. At the time of formation of aragonite, Mg\({}^{2+}\) ions acts as an impurity, which promotes the formation of aragonite crystals along with simultaneous impeding the nucleation and growth of calcite crystal. While another study carried by a group of investigators reported that the more the concentration of Ca\({}^{2+}\) ions in the solution, the higher the possibility of formation of aragonite crystals will be [24; 25; 26].