[Geography Notes] on Monazite Pdf for Exam

Monazite is a rare-earth element-rich phosphate mineral that is predominantly reddish-brown in colour.

Monzite Formula: The Monazite formula is (Ce,La,Nd,Th)(PO4,SiO4), and in igneous and metamorphic rocks such as granite, pegmatite, schist, and gneiss, it is contained in small isolated grains as an accessory mineral. These grains withstand weathering and accumulate in soils and sediments downslope from the host rock. They are mined for their rare earth and thorium content when they reach high enough concentrations.

  

Monazite price per ton- Monazite costs currently range from＄1680 to＄1900 per ton-1.

 

Is Monazite Mineral or a Group of Minerals?

Monazite chemical formula is (Ce,La,Nd,Th)(PO4,SiO4), which indicates that cerium, lanthanum, neodymium, and thorium can provide all substitutes for one another in the mineral’s structure, as well as silica for phosphate. Monazite is a mineral that is found in a number of solid-solution series with other minerals.

The term “monazite” also refers to a group of monoclinic phosphate and arsenate minerals with similar compositions and crystal structures. Below is a list of minerals that belong to the monazite group. It’s worth noting that monazite comes in a variety of forms.

Monazite Mineral Groups

 

Physical Properties of Monazite

Monazite is a resinous to vitreous mineral with a yellowish-brown to reddish-brown or greenish-brown lustre. It’s transparent, and big grains or well-formed crystals are uncommon. Where monazite is abundant locally, granular masses can be seen. It has a cleavage that is pleasant and distinct. It has a hardness of 5 to 5.5. It has a high specific gravity that varies between 4.6 and 5.4 depending on its composition.

Properties of Monazite

 

Geological Occurrence of Monazite Mineral

Monazite is known for its accumulation rather than its formation. It forms when igneous rocks crystallise and clastic sedimentary rocks metamorphose. Monazite, one of the most resistant minerals, concentrates in the weathering debris as these rocks weather. Monazite concentrations in soils and sediments near weathering outcrops can be higher than in the source rock.

The liberated monazite grains then begin their descent. They are eventually taken to a stream or a dry wash. Gravity and running water aid in the separation of hard grains of monazite and other heavy minerals from lighter minerals. They collect behind boulders, on the inside bends of stream channels, and eventually work their way down into the sediment deposit’s lower levels. Any of them flow into the sea and settle in deltaic, beach, or shallow water sediments.

Monazite Mineral Mining

Monazite mining is concentrated in placer deposits since they are easier to mine and contain higher concentrations of monazite than hard rock deposits. Gold, silver, magnetite, ilmenite, rutile, zircon, and a number of gemstones are all heavy minerals that accumulate with monazite. The recovered heavy sands are extracted to extract the heavy minerals, with the light fraction being returned to the deposit. Heavy minerals have been dredged from stream sediments, alluvial terraces, coastal sediments, beach terraces, and shallow-water sediments.

The offshore waters of India, Malaysia, Vietnam, and Brazil now contain the majority of the world’s monazite. The most extensive offshore monazite deposits are found in southern India and Sri Lanka. Australia was once the world’s largest producer of monazite, and its monazite reserve is considered to be the world’s largest. It hasn’t been a major producer since the 1990s when public opposition forced the closure of mining on Frasier Island.

In the United States, monazite is not actually mined. It was previously mined in Idaho from stream placer deposits. The Idaho batholith weathered to form these deposits. Monazite was also extracted as a byproduct from offshore deposits along the United States’ southeast coast, from North Carolina to Florida. Many states have inland and offshore reserves, but they are small and low-grade as compared to what is currently extracted in other countries.

Monazite Mineralization and Extraction

When released by the weathering of pegmatites, monazite minerals accumulate in alluvial sands due to their high density. Other heavy minerals of commercial interest, such as zircon and ilmenite, can be found in these so-called placer deposits, which are mostly sandy or fossil beach sands. Using gravity, magnetic, and electrostatic separation, monazite can be isolated as a nearly pure concentrate.

The monazite-(Ce) composition is invariably found in monazite sand deposits. In such monazites, the lanthanides usually contain 45–48 percent cerium, 24 percent lanthanum, 17 percent neodymium, 5 percent praseodymium, and trace amounts of samarium, gadolinium, and yttrium. Europium concentrations are typically low, averaging about 0.05 percent. The Lindsay Chemical Division of American Potash and Chemical Corporation, at the time the world’s largest producer of lanthanides, extracted South African “rock” monazite from Steenkampskraal in the 1950s and early 1960s.

The full collection of lanthanides was available from the Steenkampskraal monazite. Monazite’s extremely low concentrations of the heaviest lanthanides justified the term “rare” earth for these elements, which came with correspondingly high costs. Monazite’s thorium content varies, but it can reach 20–30% in some cases. Monazite derived from some carbonatites or tin ore veins in Bolivia is practically thorium-free. Commercial monazite sands, on the other hand, usually contain 6 to 12 percent thorium oxide.

1. Acid Cracking –

The initial method for extracting thorium and lanthanide from monazite was to heat it with concentrated sulfuric acid for several hours at temperatures between 120 and 150 °C. Several different methods to isolate thorium from the lanthanides were developed as a result of variations in the acid-to-ore ratio, the degree of heating, and the amount of water applied afterwards. One of the processes caused the thorium to precipitate out in the crude form as phosphate or pyrophosphate, leaving a solution of lanthanide sulphates from which the lanthanides could be quickly precipitated double sodium sulphate. The acid methods resulted in a significant amount of acid waste and a lack of phosphate content in the ore.

2. Alkaline Cracking- 

A more recent method employs a hot sodium hydroxide solution (73 percent) at a temperature of about 140 °C. The valuable phosphate content of the ore can be recovered as crystalline trisodium phosphate using this method. After treating the lanthanide/thorium hydroxide mixture with hydrochloric acid, a solution of lanthanide chlorides and an insoluble sludge of the less basic thorium hydroxide is obtained.

 

Monazite Uses

• Monazite is an important source of thorium, cerium, and other rare elements.

• It is often mined as a byproduct of heavy mineral deposits.

• Monazite sand is used in construction and casting. 

 

Rare Earth Metal Extraction From Monazite

The rare earth elements are an essential part of modern life products and green technologies. Now let’s understand how rare earth metals are extracted from monazite. The following steps below detail the extraction of rare earth metals from the monazite ore. Neutralizations and filtrations are the major requirements in this process.

1. Monazite ore should be ground to a fineness of 150 micrometres in a grinder. Monazite ore is composed of 55–60 per cent rare-earth metal oxides, 24–29 per cent P₂O₅, 5–10 per cent ThO2, and 0.2–0.4 per cent U₃O₈.

2. At input temperatures of 150 to 180 °C, pulverised monazite is blended with strongly concentrated sulfuric acid (93 per cent acid). The acid-to-ore proportion differs based on the ore’s density. The digester is stirred continuously with a powerful impeller and continues to perform at temperatures ranging from 200 to 300 °C. Before the ore, acid is compensated into the reactor and warmed. The insoluble item coats the pulverised ore grains. The heat generated by the exothermic responses raises the temperature in the reactor. The viscosity of the remedy has risen to the point where it resembles dough after 15 minutes. The product takes 3 to 4 hours to respond. Before the solution stiffens, it is removed from the digester. 

3. The components of the reactor are cooled to 70 °C and leached with 30 °C water, with a proportion of sulfuric acid to sand excluded of 1.6 to 2.5. The water-to-ore mass proportion is ten parts water to one part ore. This leaching process takes 12 to 15 hours to complete.

4. At 30°C, dilute monazite sulfate with 6–7 parts water. To establish a preferential crystallisation of thorium-phosphate cake, add NH₃(aq) to neutralise to a pH of 1.1.

5. Obtain thorium phosphate precipitate from nullified monazite solution after filtration.

6. To make condensed thorium phosphate, nourish thorium-phosphate cake through a dryer set to 120°C.

7. To generate a rare-earth-metal precipitate at a pH of 2.3, incorporate NH₃ (aq) to the remainder monazite solution.

8. To achieve a pH of 6, add NH₃ (aq) to the leftover filtrate. This results in a uranium-rich precipitate.

9. To obtain uranium concentrate, filter the leftover solution. Thorium-phosphate concentrate, RE hydroxides, and uranium concentrate are the finished products of this procedure.

 

Mineral Processing

Mineral processing is the method of separating highly valued minerals from mining waste, or sludge, in crude ores and mineral goods. It is the initial procedure that most ores go through after they are mined in order to offer a more intensive material for resource extraction metallurgy processes. Comminution and concentration are the most important functions in a modern mineral processing plant, but sampling and analysis and dewatering are also important.

In an attempt to obtain data needed for the monetary valuation of ores and concentrates, routine sampling and analysis of the raw material being handled are carried out. Modern plants also have fully automated control systems that analyse the material as it is filtered in real-time and make certain changes that are needed to produce the pure or richest possible concentrate at the verge of the lowest possible cost of operation.