Carbonate process route

Some years ago a hydrometallurgical route, called the AmMAR concept, was presented [24], The concept (Fig. 14.15) represented a general processing route for a wide variety of feed materials. The detailed design of each specific process involved a specific number of known chemical operations, combined in unique ways. The main thread was the ammonia ammonium chloride or carbonate leach solution and its extraordinary chemical flexibility. 

By using renewable carbon from biomass, an improvement in the CO2 balance can be achieved. However, significant effects beyond the impacts on greenhouse gas emissions are possible, e.g., soil modification, eutrophication, impact on biodiversity, land requirements and water consumption. These aspects depend on different factors like feedstock type, scale of production, cultivation and land-management practices, location and downstream processing routes. The environmental implications of agriculture are sometimes difficult to assess by the LCA methodology and require further research. 

The most important inorganic carbonate materials, their natural resources, and the conventional process routes were listed in Section 14.1. When the goal shifts from carbonate material production to a process that reduces C02 emissions, or fixes significant amounts of C02, then different process routes are followed, mainly because the raw materials are different. 

It is important for the discussion below to distinguish between direct and indirect process routes. Direct carbonation is the simplest approach to carbonate production (or mineral carbonation see Section 14.4) and the principal approach is that a suitable feedstock-for example, serpentine or a Ca/Mg-rich solid residue-is carbonated in a single process step. For an aqueous process this means that both the extraction of metals from the feedstock and the subsequent reaction with the dissolved C02 to form carbonates takes place in the same reactor. 

Due to the need for an extensive pretreatment of the feedstock mineral, those aqueous processes which use direct carbonation could in fact be considered as indirect. As an alternative to energy-intensive pretreatment, several groups worldwide have embarked on methods to either dissolve or leach the Mg or Ca from minerals or industrial byproducts and wastes, by using strong or weak acids (mineral or organic), alkali solutions, or ligands. [101-105]. An example of this is the process route developed by Kakizawa et al. [50] in Japan (see Section 14.3.3.2). 

SEVIN was manufactured from carbon monoxide (CO), monomethylamine (MMA), chlorine (CI2), alpha-naphthol (AN) - the first two imported by truck and the latter two made on site. The process route was as follows ... 

Low S/C Ratio - Syngas catalyst can operate with very lew steam to carbon ratio, and no externally generated steam is required for the new process route to methanol. 

Chalk is a variety of limestone mostly comprising fossilized shells from aquatic life forms. It tends to be softer than the limestone used to produce ground calcium carbonate. The most commonly utilised deposits are found in England and Denmark. Chalk is not found to a large extent in North America or Asia, so as a result the use of chalk in paper filling applications is mostly restricted to Europe. Chalk is most often produced using a dry processing route and is delivered to the mill site in dry form for makedown just prior to use. 

All raw gases produced by gasifying coal require purification and, under certain circumstances, additional conditioning before they are used as synthesis gas for methanol synthesis. The task of the purification unit is to remove gas components which are detrimental to the process route or harmful to methanol synthesis, whereas gas conditioning has the purpose of providing the proper stoichiometric conditions for producing methanol from carbon monoxide, carbon dioxide and hydrogen, expressed by the formula... 

Chemical decomposition is usually observed in solid reactions, such as carbonate, hydroxides, nitrate, acetate, oxalates, alkoxides and so on, when they are heated at a certain temperature. The decomposition leads to the formation of a new solid product, together with one or more gaseous phases, which is usually used to produce powders of simple oxides in most cases and complex oxides sometimes. Although this method has not been widely reported for the synthesis of transparent ceramic powders, it could be a potential technique for such a purpose, due to its various advantages, such as simple processing, inexpensive raw materials, and capability of large scale production. In fact, the calcination step involved in most wet-chemical processing routes, especially chemical precipitation or co-precipita-tion, is chemical decomposition, either from carbonates or hydroxides, as discussed later. 

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