Thabo Falayi

Effect of attapulgite calcination on heavy metal adsorption from acid mine drainage

Attapulgite calcined at 973.15K was characterized and utilized as an adsorbent for the removal of heavy metals and neutralization of acid mine drainage (AMD) from a gold mine. Batch adsorption experiments were carried out using a thermostatic shaker. Activated attapulgite showed that it can neutralize AMD as it raised the pH from 2.6 to 7.3 after a residence time of 2 h. Metal ion removal after 2 h was 100% for Cu (II), 99.46% for Fe (II), 96.20% for Co (II), 86.92% for Ni (II) and 71.52% for Mn (II) using a 2.5% w/v activated attapulgite loading. The adsorption best fit the Langmuir isotherm; however, Cu (II), Co (II), and Fe (II) data fit the Freundlich isotherm as well. Calcination at 973.15 K resulted in the reduction of the equilibrium residence time from 4 to 2 h, solid loading reduction from 10 to 2.5% m/v and an increase in maximum adsorption capacity compared with unactivated attapulgite.

Potassium Aluminate Geopolymerisation of Acidic Gold Mine Tailings

Acidic gold mine tailings were alkaline activated using KOH. The effect of potassium aluminate (KA) on the strength and durability of the geopolymers was investigated. A 2.8 KA:KOH geopolymer had a UCS of 18.10 MPa after curing for 5 days at 100 °C. There was an increase in UCS with an increase in loading of KA up to a ratio of 2.8. Beyond the KA:KOH ratio of 2.8, there was a 48% drop in UCS due to excess K+ ions in the system which resulted in the loss of charge balance of the system leading to reduction of UCS. It is worth mentioning that the KA:KOH ratio of 2.8 represented a Si/Al ratio of 1.02. This study showed that KA activation of acidic gold mine tailings is an attractive route to stabilise/solidify hazardous tailing material. Though there is use of elevated temperature to achieve high strength for the KA based geopolymer, this pales in comparison to energy requirements of cement manufacturing and clay brick firing.

The Strength of Lightly Cemented Power Plant Ash

Coal ash from most of Eskom power plants consists of 70–85% fly ash and 15–30% bottom ash. A total of 25 million tons of ash is produced from approximately 109 million tons of coal per annum. Small percentage of the ash were used in cement production and other construction applications and almost 80% of the ash were disposed into ash dams. The need for high volume utilization is important because of the cost of disposal and associated environmental impact. The mechanical properties of Eskom ash that were stabilized with cement was investigated. Specimens of ash were stabilized with 2% to 10% of rapid hardening Portland cement (52.5R), and compacted at two different moulding water content; (a) the optimum moisture contents of stabilized specimens (15%–19%) and (b) moisture content wet of the OMC (30%). The unconfined compressive strength (UCS), soaked UCS, secant modulus and microstructure of the stabilized specimens were evaluated. The result indicated that specimens that were compacted at 30% moisture content mobilized greater UCS than those that were compacted at OMC. For specimens that there stabilized with high cement content of 8%–10% and compacted at OMC, soaking for 24 h only indicated a marginal reduction in UCS. The increase in secant modulus with cement content was nonlinear and indicated a decreasing rate with increase in cement content. The XRD and SEM results revealed that strength development was associated with the predominance of calcium silicate hydrate (CSH) and needle shaped ettringite in cement stabilized ash. Based on limited test data, only specimens that were stabilized at 30% moisture content and with greater than 4% cement met the SANS (2007) criteria for masonry and TRH (2010) criteria for pavement backfill.