Selective fungal bioprecipitation of cobalt and nickel for multiple-product metal recovery

Summary There are a need for novel, economical and efficient metal processing technologies to improve critical metal sustainability, particularly for cobalt and nickel which have extensive applications in low‐carbon energy technologies. Fungal metal biorecovery processes show potential in this regard and the products of recovery are also industrially significant. Here we present a basis for selective biorecovery of Co and Ni oxalates and phosphates using reactive spent Aspergillus niger culture filtrate containing mycogenic oxalate and phosphate solubilized from struvite. Selective precipitation of oxalates was achieved by adjusting phosphate‐laden filtrates to pH 2.5 prior to precipitation. Co recovery at pH 2.5 was high with a maximum of ~96% achieved, while ~60% Ni recovery was achieved, yielding microscale polyhedral biominerals. Co and Ni phosphates were precipitated at pH 7.5, following prior oxalate removal, resulting in near‐total Co recovery (>99%), while Ni phosphate yields were also high with a recovery maximum of 83.0%

Evaluation of Fly Ash Reactivity Potential Using a Lime Consumption Test

The reactivity of fly ash (FA), for use in concrete, is normally evaluated in the UK/EU by means of the activity index test (on mortars at 28 and 90 d (BS EN 450-1)). This paper reports on the application of a lime consumption test, based on BS EN 196-5 (pozzolanic cement test), to determine FA reactivity more rapidly. The method uses a Portland cement (PC)/FA slurry, stored for 8 or 15 d at 40°C, and measures hydroxyl ion (OH−) and calcium oxide (CaO) concentrations of the filtrate. Seven FAs, including those produced using modern power station techniques (e.g. co-combustion, low nitrogen oxide emissions), and three PCs with different characteristics were tested. Early experiments gave acceptable repeatability for the test and revealed that pozzolanic reactions mainly occur during the initial 8 to 15 d storage. Similar behaviour for FA to that in thermogravimetric analysis and activity index tests from related studies was noted. Strong correlations were obtained for FA fineness and calcium oxide consumed (difference in calcium oxide content between PC and PC/FA with respect to that in PC). While there was general agreement for calcium oxide consumed and activity index, the correlations were poor. Similar types of effect were found to occur for mortar (activity index) and concrete. The lime consumption test can assess FA reactivity, but should be combined with measurements of the material's fineness. </jats:p