Mineralization exchange processes

The distribution of the major elements (Ca, Mg, Na, K,. ..) in soils is well known to be governed by ion-exchange processes (1). The behaviour of transition elements such as Co, Ni, Cd, Cu, etc. in natural systems (soils, sediments) often results from a combination of different effects such as precipitation, sorption in oxides, exchange in clay minerals and complexation with organic... 

Lanthanide, as a pure metal, is difficult to separate from its ores, and it is often mixed with other elements of the series. It is mosdy obtained through an ion-exchange process from the sands of the mineral monazite, which can contain as much as 25% lanthanum as well as the oxides of several other elements of the series. The metal is malleable and ductile and can be formed into many shapes. Lanthanum is considered the most basic (alkaline) of the rare-earth elements. 

Samarium is the 39th most abundant element in the Earths crust and the fifth in abundance (6.5 ppm) of all the rare-earths. In 1879 samarium was first identified in the mineral samarskite [(Y, Ce U, Fe) (Nb, Ta, Ti )Ojg]. Today, it is mostly produced by the ion-exchange process from monazite sand. Monazite sand contains almost all the rare-earths, 2.8% of which is samarium. It is also found in the minerals gadolmite, cerite, and samarskite in South Africa, South America, Australia, and the southeastern United States. It can be recovered as a byproduct of the fission process in nuclear reactors. 

Gadohnium is the 40th most abundant element on Earth and the sixth most abundant of the rare-earths found in the Earths crust (6.4 ppm). Like many other rare-earths, gadolinium is found in monazite river sand in India and Brazil and the beach sand of Florida as well as in bastnasite ores in southern California. Similar to other rare-earths, gadolinium is recovered from its minerals by the ion-exchange process. It is also produced by nuclear fission in atomic reactors designed to produce electricity. 

Of all the 17 rare-earths in the lanthanide series, terbium is number 14 in abundance. Terbium can be separated from the minerals xenotime (YPO ) and euxenite, a mixmre of the following (Y, Ca, Er, La, Ce, Y, Th)(Nb, Ta, Ti O ). It is obtained in commercial amount from monazite sand by the ion-exchange process. Monazite may contain as much as 50% rare-earth elements, and about 0.03% of this is terbium. 

Holmium is obtained from monazite, bastnasite and other rare-earth minerals as a by-product during recovery of dysprosium, thulium and other rare-earth metals. The recovery steps in production of all lanthanide elements are very similar. These involve breaking up ores by treatment with hot concentrated sulfuric acid or by caustic fusion separation of rare-earths by ion-exchange processes conversion to halide salts and reduction of the hahde(s) to metal (See Dysprosium, Gadolinium and Erbium). 

In order to obtain information about the exchange processes between the basalt and the salt, leaching experiments were performed with 1.5 m HC1 on basalt powder samples that had previously been washed in bi-distilled water in order to remove salt minerals. The H20-washed whole rock samples, as well as the resulting leachate and residue fractions have been analysed for major elements, REE, and for Sr isotopes. 

Even in this case, the use of a hybrid process combining NF, IE, and ED appears to improve the economics and performance of the tartaric stabilization of wines. For instance, Ferrarini (2001) proposed to split raw wine into a retentate and permeate by NF. The permeate, being richer in minerals, was processed by using in sequence cationic and anionic exchange resins and ED to reduce its potassium, calcium, and tartrate ion contents. By recombining the de-ashed permeate with the NF retentate, Ferrarini (2001) asserted to obtain a stabilized wine retaining almost all the flavor and aroma compounds originally present in raw wine. 

As seen previously, the acidity depends on the interlayer cation, and so catalytic activity can be affected by cation-exchange processes. In addition, when the interlayer cations, or even the cations of the octahedral sheet (e.g., Fe2+ or Fe3+), have different oxidation states, clay minerals can catalyze redox reactions, too. 

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