Mineral fertilizer production is a detailed process that involves extracting minerals from the earth, processing and refining these minerals into usable forms, and then packaging and distributing them. The result of this process is a product that helps farmers optimize crop yields and improve overall soil health.
Phosphorus fertilizers are essential for crop production as they help increase photosynthesis in plant tissue and promote the vigorous growth of plant roots. Additionally, phosphate fertilizer can help plants access both nitrogen and potassium more efficiently.
In this article, we will discuss the mineral fertilizer production process, specifically phosphate fertilizers, in detail so you can understand how it works. Additionally, we will discuss the specific types of machinery necessary for phosphorus fertilizer production and other important information related to the process.
Step 1: Extracting The Phosphate Rock for Mineral Fertilizers
The first step in the process of making phosphorus fertilizers is mining the natural sources of phosphate. This mining is done by extracting rock phosphate ore from raw material deposits worldwide. These deposits are typically found near bodies of water, such as oceans, lakes, and rivers.
The extraction process of phosphate ore typically involves using heavy machinery such as bulldozers, front-end loaders, and draglines. Bulldozers are used to clear away rocks and debris from the soil surface, while front-end loaders are used to collect the ore and transport it onto dump trucks.
In certain situations, draglines can be utilized for digging deeper deposits. A dragline is composed of a large bucket hanging from a cable that is hauled by a crane or another machine.
The explosives used in the extraction process are usually ammonium nitrate–fuel oil mixtures (ANFO.) ANFO is made up of 94% ammonium nitrate, 5% fuel oil, and 1% other ingredients. It has low explosive power compared to other explosives but is safe to use when handled correctly.
Step 2: The Beneficiation Process for Phosphate Mineral Fertilizers
Once the phosphate has been extracted from the sedimentary deposits, it must be processed to make it suitable for use in fertilizers. This process is referred to as beneficiation and involves a series of crushing, scrubbing, and milling steps. Beneficiation helps to remove impurities and separate the phosphate-containing minerals from the rock matrix.
Crushing is the first step in the beneficiation process of phosphate ore. It helps to reduce the size of the ore particles, which makes them easier to transport. It also improves the surface area of the particles, making it easier for chemical reagents to react with them during further processing.
The primary type of crusher used in phosphate mining is typically a jaw crusher, which uses compressive force to break down large chunks of material into smaller pieces. Impact crushers may also be utilized in certain cases, depending on the characteristics of the ore being processed. Both types of crushers make a grain size that can range from 0-60mm depending on the requirements of downstream processing steps.
Next, the crushed phosphate is scrubbed and screened in the beneficiation process. This is an essential step in purifying the ore before further processing. It involves removing impurities, such as clay and silica, from raw materials. The scrubbing is done by passing the ore over a series of rotating drums with a tough surface, typically of metal or rubber, with motor-driven components. As the ore passes over the angled drum, the particles rub against each other, and any dirt or clay that may be clinging to them is broken and falls off into a collection bin below.
Various machinery is used in scrubbing and screening so that the raw materials are properly purified. In addition to the drums, some machines may use centrifugal force to increase the speed at which particles separate from one another during the process. To ensure optimal results in purification, machines may also be equipped with special filters that can further remove any unwanted impurities before the ore is sent for further processing.
Once the phosphate is scrubbed and screened properly, it is milled. Rod milling is a form of grinding where rods made from steel are used to grind the phosphate rock into smaller particles. The rods are typically placed in a tumbling drum, along with water and other chemicals, which help to reduce the size of the ore particles. This process allows for greater liberation of the valuable minerals contained within the phosphate ore and increases efficiency.
Rod mills are often employed for coarse grinding operations as their sizes allow for larger feed sizes than ball mills, which allows for greater production capacity. The rods used in these mills can have varying diameters and lengths, so they can be adapted to fit different production requirements. The material being processed must be able to pass through the openings between rods or it won’t be effectively milled.
Step 3: Processing The Phosphate for Mineral Fertilizers
Once the phosphate has gone through the beneficiation process, it is reacted with sulfuric acid at high temperatures to produce phosphoric acid. This process is known as wet-process acid production or wet-processed phosphorus fertilizer.
The solution must undergo several chemical processes to create it, producing phosphorus pentoxide (P2O5) as a byproduct and then converting it into phosphoric acid (H3PO4). Once the chemical reaction occurs, ammonium phosphates are created by using natural gas or fuel to heat ammonia gas that reacts with it. This part makes different phosphates producing ammonia, such as monoammonium phosphate (MAP), diammonium phosphate (DAP), and complex fertilizers.
This part occurs rapidly and produces heat as part of its natural reaction. As a result, the temperature and pressure levels are carefully controlled and regulated for the optimal amount of acid. Reacting at these higher temperatures also helps improve the effectiveness of the reaction and allows for a shorter processing time. Additionally, careful monitoring of gas composition, particle size distribution, feed rate, and residence time can help improve the amount of acid made even further.
Step 4: Separation & Crystallization of Phosphate in Mineral Fertilizer Production
The crystallization process for phosphate is a critical step in the production of high-quality fertilizers from this ore. During crystallization, the phosphoric acid that results from heating and reacting with sulfuric acid is cooled to form crystals. This helps to facilitate the filtration and purification of impurities by making them more visible and easier to collect.
Cooling the acid causes it to solidify into small crystal particles that can be collected for further balanced fertilizer use. The size of these crystals typically ranges between 0.01mm – 0.1mm, so they must be filtered very carefully so that no contaminants remain in the final product.
During this step, substances like fluoride may be added to improve the quality of phosphorus-containing fertilizers as plant food. Adding it during this stage helps decrease levels of toxic materials in the phosphate.
It is also known to increase high-value crops and overall plant growth, so it has become more popular as a supplement for increasing plant nutrition and productivity in agricultural practices. It is an alternative to potassium fertilizers, which can contain potassium chloride, potassium sulfate, or potassium nitrate.
Additionally, fertilizers containing phosphorus can also be a substitute for nitrogen-based fertilizers, which can be high in chemical properties like ammonium sulfate or nitric acid.
Step 5: Quality Assurance & Distribution To Make Phosphate Fertilizer
After it has completed all steps of production, the final phosphate product is tested for quality assurance. Quality control tests are conducted using chemical methods such as titration or colorimetry to determine whether there are any impurities present in the product. Physical tests may also be conducted on finished products, such as granularity analysis or sieve test, to check if they meet size or shape requirements.
Why Phosphorus Fertilizer is Popular in Agriculture
Once the phosphorus product is incorporated into fertilizer, it is distributed around the world. They contain essential plant nutrients for growing crops but also help maintain soil fertility and plant uptake. Phosphorus allows plants to absorb other vital elements, such as nitrogen and potassium, in addition to helping with seed germination and root growth as well.
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If you are looking for mineral processing equipment, we can help at Kemper Equipment. Our experience in designing and building a variety of fertilizer product operations is unmatched throughout the material handling industry, making us the choice of many for over 40 years. Contact us today to get started and see the Kemper difference!