Overview of research in critical and precious metal recovery using biosorption, application to real-life wastes and uses of the metal-loaded materials.

The study determined the levels of some heavy metals and pH, organic matter and particle size distribution of soil within the vicinity of Gboko abattoir. Soil samples were collected at depth of 0-20 cm and analyzed using standard laboratory methods. The results of AAS analysis of the heavy metals showed that the soil had mean value of Zn²⁺ 3.0195 ppm, Pb²⁺ 0.5413 ppm, Ni²⁺ 0.1949 ppm, Cr³⁺ 0.1134 ppm and Cd²⁺ 0.0185 ppm. These values were higher than similar results obtained from the control soil but the mean levels of the metals were lower than the permissible limits set by the Nigerian Department of Petroleum Resources (NDPR) and European Union (EU) respectively. The soil heavy metals were positively correlated. The mean pH of the soil (6.03) indicates acidity, the organic matter was very high and the particle size distribution revealed sandy-loam texture. The results of the analysis showed some levels of pollution which indicated that the activities at the abattoir were contributing to the pollution load of soil in the environment. It is therefore, recommended that the activities at the abattoir should be monitored closely by relevant agencies in order to prevent full-blown environmental problems in the near future and avert the attendant health hazards.

Gelatinization temperature of starches from different varieties of cereals, deep-red sorghum, red sorghum, white sorghum, mixed sorghum, white fonio (Digitaria exilis), black fonio (Digitaria iburua), Eleusine coracana (tamba), proso millet (p. miliacium), brown top millet (p. ramosum) and finger millet (Eleusine coracana) were determined by electrical conductivity (EC) method. Among the untreated starches, the results showed that tamba recorded the least onset and peak gelatinization temperatures of 53.0 o C and 63.0 o C respectively while the highest onset gelatinization temperature, 76 o C was recorded with proso millet. Proso millet and finger millet had the highest peak gelatinization temperature. deep-red sorghum and red sorghum had the least end gelatinization temperature while proso millet recorded the highest value. The 0.1MKCl treatment of cereals starches produced elevated onset gelatinization temperatures (62.0-78.0 o C). Mixed sorghum had the least onset gelatinization temperature while proso millet and finger millet recorded the highest gelatinization temperature. Following the 0.1MKCl treatment, starches from tamba and proso millet recorded the least and highest peak gelatinization temperatures respectively. Deep-red and red sorghum recorded the least end gelatinization temperatures while proso millet, brown top millet and finger millet recorded the highest end gelatinization temperatures. The treatment of the cereals starches with 0.10MKCl significantly (p < 0.05) delayed the onset gelatinization temperature of the starches and narrowed the gelatinization temperature range. The results of the conductivity of both the 0.1MKCl treated and untreated starch showed nonlinearity within the gelatinization range. This finding has important implication on the energy and time requirement to gelatinize the starch for specific industrial use.

Furthermore, industries generate a variety of wastes which contain heavy metals [7]. Electroplating and mining companies generate large amounts of mercury, lead, cadmium, silver, copper, and zinc ions [8,9]. More so, papers, metals, electrical and electronic equipment wastes contain precious metals like Ag, Au [10]. And some of these metals are regarded as technology metals [11,12]. Unfortunately, the reserves of highgrade ores of these metals are depleting [7]. Therefore, there is a need to recycle and recover these metals from the environment. Moreover, some heavy metals can be hazardous even at low concentrations [9,13]. According to Nagajyoti et al. [14] heavy metals such as Cd, Cu, Pb, Cr and Hg are major environmental pollutants, particularly in areas with high anthropogenic activities. Thus, when these metals are in bioavailable forms and at excessive levels, they have the potential to become toxic to plants and consequently the environment [14]. In addition, there are usually trace amounts of iron, copper, manganese, calcium, and other metals found naturally in many raw materials [15,16]. These metal ions are normally found in processing water as well, and may infiltrate processing [15]. Moreso, presence of metal ions in a process or product can bring about scaling, chemical degradation, discoloration, precipitation, emulsion instability, rancidity, and reduce; quality, consumer appeal, shelf-life and ultimate value [15,17,18].Fortunately, chelating agents have been used to eradicate these problems by binding metal ions via N, O, S atoms as the case may be [19]. When metal ions are bonded to chelant, the metal becomes blocked from undesired interaction [20].

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