Abstract
Mono-calcium phosphate (MCP) is a substance which has many uses such as being used as baking powder, fertilizer, firming agent and phosphate feed supplement. However, the current method of synthesizing MCP involves the reaction between phosphate rock and phosphoric acid which causes environmental damage because it produces toxic gases such as hydrogen fluoride. Hence the current study proposes to synthesize MCP using a more environmentally method, by replacing phosphate rock with blood cockle shells which have a high content of calcium carbonate and thus could potentially react with phosphoric acid to yield MCP. To determine the optimum volume of phosphoric acid and mass of cockle shell to obtain the maximum yield of MCP, reactions using different volumes of phosphoric acid were carried out. Results show that 5g of blood cockle shell reacted with 50 ml of 2M phosphoric acid to produce the greatest yield of MCP. Heating duration of more than 30 minutes results in a lower yield of MCP. The MCP synthesised contained 25-27% phosphorus and 21-23% of calcium content and was also found to have a positive effect on plant growth, increasing plant height by 47%, fresh weigh by 46% and dry weight by 33%. Hence, blood cockle shell waste is a viable green alternative to the conventional phosphate rocks in the production of MCP.
What is Mono-Calcium Phosphate?(MCP)
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Current method of synthesising MCP
Mono-calcium phosphate (MCP) is a substance commonly used as baking powder, fertilizer, firming agent and phosphate feed supplement. The current method of producing mono-calcium phosphate fertilizers is by the treatment of "phosphate rock" with acids. Using phosphoric acid, fluorapatite present in the rocks is converted to Ca(H2PO4)2 and is called triple superphosphate [5]. The reaction is shown in equation (1)
Ca5(PO4)3F + 7 H3PO4 → 5 Ca(H2PO4)2 + HF (1) However, the current method of producing MCP requires the mining of phosphate rocks which in turn causes serious environmental damage. The process of mining also requires labour and cost of machineries and planning are also high. Moreover, the highly toxic hydrogen fluoride (HF) which is produced as a by-product is a severe irritant to the eyes, skin, and nasal passages where high concentrations may penetrate to the lungs, resulting in edema and haemorrhage [6]. The toxic hydrogen fluoride will also cause air pollution. Therefore, a cheaper and more environmentally friendly method is needed to produce MCP. Rationale for choosing cockle shells
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Blood cockle shell, which is rich in calcium carbonate, can be a potential starting material for the synthesis of MCP. Calcium carbonate reacts with phosphoric acid, a tribasic acid, in 3 possible reactions, as shown in equations (2) to (4).
CaCO3 (s) + 2H3PO4 (aq) → Ca(H2PO4)2 (aq) + H2O (l) + CO2 (g) (2)
CaCO3 (s) + H3PO4 (aq) → CaHPO4 (s) + H2O (l) + CO2 (g) (3)
3CaCO3 (s) + 2H3PO4 (aq) → Ca3(PO4)2 (s) + 3H2O (l) + 3CO2 (g) (4)
As calcium carbonate is the main substance reacting with phosphoric acid, there will probably not be highly toxic gas produced as a by-product. Furthermore, as no mining is required, this method of synthesizing MCP is more environmentally friendly and potentially of lower cost as one of the starting materials is derived from wastes. This study, if successful, would help reduce waste and at the same time produce a useful product. MCP contains calcium (a micro plant nutrient) and phosphorus (a macro plant nutrient) which could be used as plant fertilizers to enhance plant growth.
The desired reaction is the first one (equation (2)), of which a soluble product can be obtained that can be easily absorbed by plants. In this study, ratio of mass of cockle shell to volume of phosphoric acid (2 M) used was varied to determine the suitable ratio which will yield the soluble MCP as the major product of the reaction. The calcium and phosphorus content of the synthesized MCP was analysed. Finally the effectiveness of the synthesized MCP as a plant fertilizer was also evaluated and compared with that of commercial MCP.
CaCO3 (s) + 2H3PO4 (aq) → Ca(H2PO4)2 (aq) + H2O (l) + CO2 (g) (2)
CaCO3 (s) + H3PO4 (aq) → CaHPO4 (s) + H2O (l) + CO2 (g) (3)
3CaCO3 (s) + 2H3PO4 (aq) → Ca3(PO4)2 (s) + 3H2O (l) + 3CO2 (g) (4)
As calcium carbonate is the main substance reacting with phosphoric acid, there will probably not be highly toxic gas produced as a by-product. Furthermore, as no mining is required, this method of synthesizing MCP is more environmentally friendly and potentially of lower cost as one of the starting materials is derived from wastes. This study, if successful, would help reduce waste and at the same time produce a useful product. MCP contains calcium (a micro plant nutrient) and phosphorus (a macro plant nutrient) which could be used as plant fertilizers to enhance plant growth.
The desired reaction is the first one (equation (2)), of which a soluble product can be obtained that can be easily absorbed by plants. In this study, ratio of mass of cockle shell to volume of phosphoric acid (2 M) used was varied to determine the suitable ratio which will yield the soluble MCP as the major product of the reaction. The calcium and phosphorus content of the synthesized MCP was analysed. Finally the effectiveness of the synthesized MCP as a plant fertilizer was also evaluated and compared with that of commercial MCP.
Objectives:
- 1. To synthesise monocalcium phosphate (MCP) from blood cockle shells using phosphoric acid
CaCO3(s) + 2H3PO4(aq) -> Ca(H2PO4)2(aq) + H2O(l) + CO2(g)
3. Determine the calcium and phosphorous content in MCP synthesised
4. Characterise the MCP using XRD (X-ray diffraction) and SEM (Scanning electron microscope)
5. To evaluate effectiveness of synthesised MCP as a plant fertilizer
Hypothesis:
- Monocalcium phosphate (MCP) can be synthesised from blood
- cockle shells and is an effective fertiliser