What are fertilizers ?

What are fertilizers ?

Chemical fertilizers (the so-called black manure and white manure) play a role in providing about 40 to 60% of the world’s food resources. Chemical fertilizers include one or more food sources needed by plants, which can exist in all three forms of solid, liquid or gas phases. These compounds can also be added to the soil,It can be sprayed directly on the plant itself (plant leaves) or it can be dissolved in water and added to the soil of the plant. The use of these materials is used to improve the quality of the soil, increase the amount of the product or improve the quality of the produced product. The use of these fertilizers dates back to the 19th century. When the agricultural industry expanded, the amount of animal or vegetable fertilizers needed was limited. The first attempts to produce chemical fertilizers on an industrial scale from the extraction of potassium from German mines began in 1860, around the same years, the first production unit of phosphate chemical fertilizers from urea phosphate was also formed on a commercial scale. Inorganic fertilizers can be divided into three general categories: nitrogen, phosphate and potash

White chemical fertilizer contains nitrogen in the form of nitrate, which is necessary for the growth of many plants, and for this reason, this fertilizer can be used to help the growth of a wide range of plants. It has a very good dissolution ability and easily dissolves in water and is quickly available to the plant.

After nitrogen fertilizers, this type of chemical fertilizer is considered the most widely used type of fertilizer in the world. These compounds are necessary for the proper growth of plant roots. They help to increase the harvest yield and increase the resistance of plants against various diseases. Black chemical fertilizer provides phosphorus element for all kinds of plants, including potted plants, trees and crops.

Some nitrogen fertilizers are:

How to produce

These fertilizers are often obtained from natural gas. During several stages, natural gas, especially methane, is combined with nitrogen in the air to produce nitrogen fertilizers. Note that 80% of natural gas is used to make nitrogen fertilizers. While only 20% of gas is used for heating processes and electricity generation With the help of this gas, two basic materials, ammonium nitrate and urea, are produced, and then by adding different types of additives, different nitrogen fertilizers can be produced. For example, phosphorus and potassium additives are used to make complete fertilizer. Dolomite additive is used to form CAN, or UAN can be produced by mixing urea and ammonium nitrate solution.

Some phosphate fertilizers are:

  • Diammonium phosphate
  • Mono ammonium phosphate
  • Simple superphosphate
  • Triple Super Phosphate

How to produce

Phosphate fertilizers are produced by acidifying phosphate rocks. It should be noted that phosphate rock is not soluble by itself and therefore cannot provide phosphorus to the plant. Most of the sources of phosphorus are sediments on the ocean floor that were later uplifted by land flooding. These sediments can contain various minerals, so contamination of these rocks with heavy metals such as cadmium is another issue that should be considered. Other sources of phosphate rock are igneous rock deposits obtained from molten lava of volcanoes. This source contains less pollutants. The Yara mine in Finland is considered a good source for obtaining this type of phosphate rock. As mentioned, these stones are processed with acids such as phosphoric, sulfuric or nitric. The use of each of the mentioned acids has its own advantages and disadvantages. For example, the use of sulfuric acid produces phosphorus fertilizers with a low concentration, among these substances, simple superphosphate can be mentioned. However, the use of phosphoric acid can produce higher concentrations of these substances. The use of nitric acid leaves almost no residue and produces two fertilizers 

1- Nitrophosphates, which are combined with potassium to produce NPK complex fertilizers such as Yara Mila.

2-Calcium nitrate, which is obtained from the combination of nitric acid with calcium in phosphate rock.

It should be noted that the limitation of using nitric acid is that when using it, the amount of phosphate in the fertilizer cannot exceed the amount of nitrogen. Types of black manure and its production method,  In the following, we will introduce the types of these compounds and their production methods:  

The production of superphosphate from apatite and sulfuric acid is ideally done according to the following equation: 

2Ca5[(PO4)3F]+7H2SO4——–> 3Ca(H2PO4)2+7CaSO4+2HF 

The production reaction of this chemical fertilizer is carried out in two stages: in the first fast stage, anhydrite and phosphoric acid are created. Then this phosphoric acid slowly (within a few weeks) reacts with excess apatite and hydrous monocalcium phosphate is produced. A part of fluoride (about 10-40%) in apatite is removed in the form of gaseous silicon tetrafluoride, and the rest remains in superphosphate. Any carbonato-apatite or calcium carbonate in the fluoro-apatite will generate carbon dioxide. In fact, the industrial production of super phosphate (black fertilizer) is done in five stages, 

(1) Grinding apatite
(2) Reaction with sulfuric acid
(3) Freezing and crushing the initial reaction product
(4) hardening (setting) – completion of the reaction
(5) possible powdering and granulation of the final product

Triple superphosphate is produced based on the following equation: 

2Ca5[(PO4)3F]+14H3PO4 ———->10Ca(H2PO4)2+2HF

The industrial production of this black fertilizer is very similar to the production of superphosphate. Milled apatite (with P2O5≤31%) (74µm>70% and acid method (with 52-54% P2O5) are used as starting materials. The molar ratio of Cao to P2O5 should be in The final product is 0.95-0.92 and the amount of P2O5 is about 47%. The freezing of the reaction mixture takes place faster than it does in the production of superphosphate

The following ammonium phosphates are used as fertilizers (separately or mixed) 

  • Mono ammonium phosphate (NH4H2PO4   (MAP)
  • Diammonium phosphate (NH4)2HPO4 (DAP)
  • Ammonium polyphosphate (NH4PO3)n ( APP)

Triammonium phosphate is not a commercial product due to its high ammonia vapor pressure. Mono and diammonium phosphate are used as solid fertilizers, while ammonium polyphosphate is mainly used as a solution and as a liquid fertilizer. Because this substance is granulated unlike orthophosphates. In addition, due to its complexing properties, it keeps impurities (iron, aluminum, magnesium, etc.) in solution. Ammonium phosphate fertilizers are relatively impure (about 85% purity). This issue is attributed to the use of unrefined acid in their preparation.

The gradual dissolution of apatite with nitric acid is of commercial importance, as is the gradual dissolution of apatite with sulfuric acid (creating phosphoric acid or superphosphate) or with phosphoric acid (creating ternary superphosphate) In contrast, hydrochloric acid is not important in this regard. Basically, the exothermic reaction with nitric acid proceeds as follows: In this process, 50-60% nitric acid (up to 20% extra) is used. Fluorine mostly remains in the reaction mixture. A part of nitric acid is reduced to nitrogen oxides, which must be removed from waste gases. Unlike the gradual dissolution of apatite with sulfuric acid, in this case calcium is present in solution. Since calcium nitrate is highly precipitated, it must be converted or separated and then used. In the Lonza AG method, calcium nitrate remains in the mixture. The mixture (gradual dissolution) is dehydrated to the extent that there is no more than 2 to 3 moles of water per mole of calcium nitrate. Then the resulting mass, which has not yet hardened, is granulated and covered with alkaline slag (Thomas feed), calcium cyanamide, etc.

Production method of nitrophosphates

The process of producing this chemical fertilizer can be done as follows:

► As a result of adding ammonia and carbon dioxide to the reaction mixture, as a result, in addition to calcium carbonate, ammonium nitrate and calcium hydrogen phosphate (dicalcium phosphate) only soluble in citrate will be produced (carbonitric process): 

3H3PO4+5Ca(NO3)2+10NH3+2CO2+2H2O ——> 10NH4NO3+2CaCO3+3CaHPO4

◄ or by adding sulfate in the form of sulfuric acid, ammonium sulfate, or potassium sulfate, as a result, calcium is converted into calcium sulfate in a similar reaction. As a result of neutralization, free phosphoric acid creates calcium hydrogen phosphate (sulfonitric process).

Potash fertilizers (K)

The chemical fertilizer containing potassium element is called white fertilizer. Its types include potassium chloride (KCl), potassium nitrate (KNO3) and potassium sulfate. This type of fertilizer also helps the overall growth of the plant, especially the growth of its roots, and increases its resistance to various diseases.

Some potash fertilizers

  • Potash fertilizer
  • Potassium sulfate
  • Potassium chloride

How to produce

Most of the potassium used in the production of fertilizers is obtained from natural deposits of potassium chloride, and then the pieces of rock and salt are removed from it. Deposits of potassium sulfate and potassium nitrate are also considered as other sources of these fertilizers, which are rarer. However, if these sources are used, the stones and salt in them should be removed. One of the main sources of potassium chloride is the Dead Sea.

The amount of consumption and the growth of the use of different fertilizers

Nitrogen fertilizers (white manure) are still the most widely used type of these fertilizers in the world. But in the past years, the consumption of potassium and phosphate fertilizers (so-called black manure) has also increased. Among the most important reasons for the increase in the consumption of chemical fertilizers during these years, we can mention the increase in the population, change in eating habits, change in the farming method, which demands to harvest more crops per cultivated hectare, the amount of consumption of these three different types of chemical fertilizers varies depending on the type of product produced in different regions around the world

Guide to choosing the right chemical fertilizer

Many fertilizers available in the market today contain all three essential elements required for plant growth mentioned above, and they are called complete fertilizers. It must have happened to you that when you buy this type of chemical fertilizers, you see its percentage composition in the form of three numbers in a row on its packaging in the information section of the type of fertilizer. But what are these numbers? These numbers actually represent the amount of nitrogen, phosphorus and potassium elements in that fertilizer, and according to the type of your plant’s needs, you can choose the chemical fertilizer (so-called black fertilizer or white fertilizer) suitable for the plant according to this. Choose the numbers that represent its percentage composition.

Disadvantages of chemical fertilizers

Chemical fertilizers have positive effects on the amount of production of agricultural products and as a result the economy of countries. However, the use of these chemicals also has disadvantages, which are mentioned below:

  • Chemical fertilizers affect the microorganisms that live in the soil. The acidity of these materials changes the pH of the soil and thus changes the micro-organisms in the soil. Long-term use can cause the growth of pests and the destruction of microbes in the soil.
  • These codes are generally completely soluble in water, and some of them enter the ground water without any special effect on the plant. When the water is polluted, the chemicals reach the lower layers of the soil and there, in contact with the clay, it creates an impenetrable and hard layer of soil.
  • Chemical fertilizers provide plants with a large amount of compounds such as nitrogen and phosphorus in a short period of time. The presence of these elements in connection with each other can cause disease in the plan.
  • Although the use of these fertilizers has many advantages for the plant and its growth, it has no advantage for the soil and its long-term use can destroy the soil.
  • The use of excess nitrogen causes the production of greenhouse gases and nitrous oxide and their entry into the atmosphere. Generally, the amount of production of these gases is higher than the amount absorbed by plants, and as a result, they will bring effects such as global warming.
  • One of the concerns about the continuous use of these materials is the depletion of the soil from essential materials. As a result, chemicals produced from these soils contain less vitamins and minerals.

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