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Van der Ent et al-2015-Agromining -- Farming for metals in the future-ES&T+Cover
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Globally, $25-50 billion is spent each year cleaning up sites contaminated with heavy metals. Because traditional cleanup methods such as incineration, chemical treatment, and excavation and removal are costly and can damage the environment, metal-hyperaccumulating plants (plants that accumulate >0.1% heavy metals in leaves or other tissues) may be a more cost-effective, less-intrusive option for remediating such sites. Members of the Brassicaceae comprise 25% of metal-hyperaccumulating species worldwide discovered to date and are potential candidates for phytoremediation technologies. Here we describe the diversity of metal-hyperaccumulating species in the Brassicaceae and discuss the physiological mechanisms of metal uptake and tolerance, the genetic basis for the metal tolerance mechanisms, ecological consequences of metal hyperaccumulation, and the role of the Brassicaceae species in remediating contaminated sites worldwide.
Keywords:
Green technology, hyperaccumulation, metal tolerance, phytoremediation, ultramafic soil
The precipitation of mixed hydroxide is increasingly being considered as an intermediate step in the hydrometallurgical processing of nickel and cobalt. Producers currently receive roughly 75% of the value of the contained nickel and zero value for contained cobalt. In this paper, a new selective leach process for refining the mixed hydroxide is described that allows for recovery of the majority of the nickel as final metal product and realizes value for the cobalt. The features of the new process are compared with two other alternative routes (1) acid leaching followed by solvent extraction of the cobalt and (2) ammonia leaching followed by solvent extraction of the nickel. The outcomes of a process simulation for the selective acid leaching process are presented along with capital and operating cost estimates. The operating and capital costs of the process are estimated to ±50%. For the processing of 50,000 t-Ni/y in the form of MHP, the operating cost is estimated to be $93 million AUD ($0.87 per lb of Ni contained in MHP) and the capital cost as defined for this study is estimated to be $287 million AUD. A new 20 year plant processing MHP would have a payback period of less than 2 years, an IRR of over 60% and an NPV of greater than $1.5 billion AUD. Over 94% of the total value (nickel and cobalt) contained in the MHP is extracted by the new process.
Botanical exploration of serpentine soils in Turkey and neighbouring countries has shown that the region includes at least 59 taxa capable of hyperaccumulating nickel (to >0.1% of plant dry weight). These hyperaccumulators belong to the Brassicaceae (Aethionema R.Br., Alyssum L., Bornmuellera Hausskn., Pseudosempervivum (Boiss.) Grossh. (Cochlearia L.), and Thlaspi L. s.l.) and the Asteraceae (Centaurea L.). We review present knowledge of the hyperaccumulators and provide additional data recently obtained. Some species are serpentine-endemic and invariably Ni hyperaccumulating; others show more complex distribution and Ni-accumulating behaviour. Many are good subjects for biochemical studies on the Ni-accumulation and sequestering processes. There is potential in Turkey for exploiting Ni hyperaccumulation for remediation of Ni-contaminated soils ('phytoremediation') and for economical selective extraction of metal compounds by cropping hyperaccumulators ('phytomining'). However, there is a need for further exploration of the natural resources and some further taxonomic work by traditional and DNA methods. Attention must be paid to conservation issues, as some of the relevant species are quite rare.
Pressure leaching of nickeliferous laterites by sulfuric acid is the key to the utilization of ores at Moa Bay, Cuba. This is a description of operations at Freeport Nickel’s new plant in Cuba.
As indicated in the title, this article gives brief statements of investigations of various fundamental and practical factors of the ammonia leaching process for nickel and cobalt ores. The process was in large scale operation at Nicaro, Cuba, as an emergency measure in World War II. Descriptions of this plant and its operation have been published but these descriptions mainly covered installation and working scale results, and the present article gives a considerable amount of hitherto unpublished data on various phases of the method, including conditions for ore reduction, leaching, distillation, etc. Possibilities as to further development and results of tests on ores other than the Cuban laterites are also included.
Wastes may supply enough macronutrients to act as N, P, or K fertilizers and provide optimum macronutrients in forage plants. Alternatively, the waste may provide N at a C:N ratio that causes nitrogen deficiency and low protein levels. Macroelement fertility balance must be managed carefully to obtain both optimum plant growth and forage quality. Use of sewage sludge as N and P fertilizer has led to severe K deficiency unless K fertilizer is supplied. Woody wastes cause severe N deficiency unless adequate N is supplied or the wastes are composted with N fertilizer before application. Some microelements are so insoluble or strongly sorbed in soil that plant shoots do not have significantly increased concentrations of the elements even when soils are greatly enriched. These and other aspects of the subject are reviewed in the paper, which emphasizes management of land treatment sites. Refs.
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February 2015