The principal neurons of the medial superior olive (MSO) are considered to be responsible for transforming the temporal information present in the binaural acoustic stimulus into an output encoding sound location along the horizontal axis. Spatial resolution of sound localization depends critically on the time resolution with which MSO neurons can detect microsecond differences in the timing of inputs from the two ears. This fast temporal processing is contingent on voltage gated ion channels. The work presented in this thesis demonstrates that two currents, namely a hyperpolarization activated cationic current and low voltage activated potassium current dynamically interact to regulate the intrinsic time resolution of MSO neurons. We observe that the ability of MSO neurons to perform sub-millisecond temporal processing matures after birth, especially around the time of the clearing of the auditory canal. Hyperpolarization activated cationic current was found to be one of the underlying mechanisms transforming slow immature MSO neurons into temporally precise adult MSO neurons. / text

Porous, high surface area activated carbon (AC) can be used to remove certain irritating and toxic gases from contaminated air streams. Impregnating AC with carefully selected chemicals can improve ACs adsorption capacity for certain gases and provide adsorption capacity for gases that un-impregnated AC cannot fi lter. Impregnated activated carbons (IACs) and ACs can be used as the active component in respirators. Comparative studies of di fferent commercially available AC samples and of IAC samples, prepared from a wide variety of di fferent chemicals, were performed. The gas adsorption capacity of the samples was tested using sulfur dioxide (SO2), ammonia (NH3), hydrogen cyanide (HCN) and cyclohexane (C6H12) challenge gases and compared to results obtained from a commercially available broad spectrum respirator carbon. The samples were characterized using wide angle x-ray di raction (XRD), small angle x-ray scattering (SAXS), nitrogen adsorption isotherms, thermal gravimetric analysis (TGA) and scanning electron microscopy (SEM). Highlights of this work include the discovery of a IAC sample prepared from zinc nitrate (Zn(NO3)2) and nitric acid (HNO3) that, after heating at 180 C under argon, had overall dry gas adsorption capacity that was greater than the commercially available sample. The importance of pore size on the C6H12 adsorption capacity of AC was demonstrated using SAXS and nitrogen adsorption data. A relationship between decreased humid C6H12 capacity and pre-adsorbed water was shown using SAXS, TGA and gravimetric studies.

abstract: The production and applications of engineered nanomaterials (ENM) has increased rapidly in the last decade, with release of ENM to the environment through the sewer system and municipal wastewater treatment plants (WWTPs) being of concern. Currently, the literature on ENM release from WWTPs and removal of ENM by WWTPs is insufficient and disorganized. There is little quantitative data on the removal of multi-walled carbon nanotubes (MWCNTs), graphene oxide (GO), or few-layer graphene (FLG), from wastewater onto biomass. The removal of pristine and oxidized MWCNTs (O-MWCNTs), graphene oxide (GO), few-layer graphene (FLG) and Tween™ 20-coated Ag ENM by the interaction with biomass were determined by programmable thermal analysis (PTA) and UV-Vis spectrophotometry. The removal of pristine and O-MWCNTs was 96% from the water phase via aggregation and 30-min settling in presence or absence of biomass with an initial MWCNT concentration of 25 mg/L. The removal of 25 mg/L GO was 65% with biomass concentration at or above 1,000 mg TSS/L. The removal of 1 mg/L FLG was 16% with 50 mg TSS/L. The removal of Tween™ 20 Ag ENM with concentration from 0.97 mg/L to 2.6 mg/L was from 11% to 92% with biomass concentration of 500 mg TSS/L to 3,000 mg TSS/L, respectively. A database of ENM removal by biomass was established by analyzing data from published papers, and non-linear solid-liquid distribution functions were built into the database. A conventional activated sludge (CAS) model was built based on a membrane bioreactor (MBR) model from a previous paper. An iterative numeric approach was adapted to the CAS model to calculate the result of non-linear adsorption of ENM by biomass in the CAS process. Kinetic studies of the CAS model showed the model performance changed mostly in the first 10 days after changing influent chemical oxygen demand (COD) concentration, and reached a steady state after 11 days. Over 60% of ENMs which have distribution coefficients in the database reached higher than 50% removal by the CAS model under general operational conditions. This result suggests that traditional WWTP which include the CAS process can remove many known types of ENMs in certain degree. / Dissertation/Thesis / Masters Thesis Civil and Environmental Engineering 2015

Tertiary treatment methods were tested on secondary effluent from an abattoir biological wastewater treatment plant with the purpose of renovating it for re-use in the abattoir. The colour and dissolved organic matter could be removed to such an extent that the water would comply with water of insignificant health risk (Department of Health). The treatment process sequence proven to be effective in upgrading this water so insignificant health risk standard were coagulation with a polymer blend, separation, ozonation, filtration and activated carbon filtration. The development of biologically activated carbon in practice was accepted as inevitable and desirable for optimum water quality, but not tested. A deciding factor in the selection of an appropriate treatment was that the final water would also have acceptable corrosion properties. / Dissertation (MSc)--University of Pretoria, 2010. / Chemical Engineering / unrestricted

Les gliomes sont les tumeurs cérébrales les plus fréquentes chez l’adulte. Il s’agit d’un groupe de tumeurs hétérogène pouvant être classées dans différents sous-groupes selon des critères moléculaires et histopathologiques, donnant une indication sur leur agressivité. Les p21-activated kinase (PAK) sont des sérine-thréonine kinases effectrices des GTPases Rac et Cdc42 et font ainsi partie de nombreuses voies de signalisation. Elles régulent de nombreuses voies d’intérêt dans la biologie des cancers, comme les voies Mek/Erk, PI3K/Akt et Wnt/b-caténine. PAK1 est fréquemment surexprimé et/ou suractivé dans plusieurs cancers, notamment du sein, des ovaires de la prostate et du cerveau, alors que PAK3 induit la sortie du cycle cellulaire et la différenciation des cellules au cours de la neurogenèse dans plusieurs modèles animaux. Durant ma thèse, j’ai pu observer que l’expression de PAK3 était de bon pronostic pour les patients atteints de gliomes, et était plus élevée dans un sous-type de tumeurs caractérisé par la codélétion 1p/19q. In vitro, l’expression de PAK3 était plus élevée dans une lignée de cellules de gliome de signature proneurale, non tumorigène après xenogreffe chez la souris. Au cours de la différenciation des cellules de gliome, l’augmentation de l’expression de PAK3 est associée avec des marqueurs de lignage neural et neuronal. L’inhibition de l’expression de PAK3 entraîne l’augmentation de la capacité d’auto-renouvellement et de la tumorigénicité d’une lignée de cellules de gliome, et favorise la différenciation gliale des cellules. / Gliomas are the most common and lethal adult primary brain tumors. Their complex heterogeneity is evidenced by numerous genomic studies showing distinct molecular entities in glioma. P21-activated-kinases (PAK) are serine threonine kinases involved in multiple signal transduction pathways as downstream effectors of Rac and Cdc42. They regulate several key cancer-relevant pathways like cell division and movement. PAK1 and PAK3 are highly expressed in the brain; PAK1 is frequently overexpressed and/or over-activated in several human cancers whereas PAK3 is involved in neural differentiation and the developmental proneural pathway. The role of these two kinases in brain tumor pathophysiology is unknown. We have observed that PAK3 expression was associated with a longer survival for patients with glioma and was higher in 1p/19q gliomas. In vitro, PAK3 was highly expressed in a glioma cell line with a proneural signature that did not induce tumor after xenograft. Its increasing expression upon a set of differentiation paradigms was correlated with those of neural and/or neuronal markers in glioma cell lines. Inhibition of PAK3 expression increased cell renewal and tumorigenicity. It impaired cell differentiation, promoting the glial lineage.

Analytical analyses conducted at the Himmerfjärden WWTP (285.000 PE connected) identified 70 pharmaceutical compounds belonging to different therapeutic classes. Such organic micropollutants at low detected concentration range of µg - ng l-1 did not affect the treatment processes at WWTP. Results from analytical studies indicated continuous discharge of organic micropollutants to the surface water with a calculated load amounting to 1.51 kg day-1. Metoprolol, carbamazepine and naproxen were chosen for testing different removal methods. Oxygen Uptake Rate (OUR) tests were conducted to assess the bacterial activity of an activated sludge taken from a full scale aeration plant with the presence of selected target compounds. A semi-technical scale membrane bioreactor ZeeWeed10™, treating final effluent from the Himmerfjärden WWTP (Sweden) was seeded with activated sludge from full scale biological stage. The membrane bioreactor (MBR) system placed after the final treatment appeared to be an insufficient technology for removal of residual amounts of organic micropollutants from WWTP effluents. Batch test studies with activated sludge taken from the membrane bioreactor and with application of granular activated carbon (GAC) filtration resulted in giving an overall assessment of removal efficiency. Metoprolol and carbamazepine tend to be resistant to the biodegradation process and in the dosed high concentration lead to bacterial cell decomposition in the activated sludge. Apparently, removal efficiency for naproxen exceeded the value of 46% with the spiked initial amount of 3.3 mg NAP g-1 MLSS. Application of the GAC filtration proved to be an efficient technique for removal of pharmaceutical compounds from treated wastewater. Application of the statistical programme Modde7 was a time saving tool in studies of fouling occurrence. The effect of fouling phenomenon, which is a highly limiting factor for MBR performance, was minimised by adjusting the operational parameters as predicted by the Modde7 programme. / QC 20101104

Equilibrium powdered activated carbon (PAC) concentrations of 20, 160, and 280 mg/L in activated sludge reactors treating cellulose acetate manufacturing wastewater were found to enhance substrate removal. The improved substrate removal as measured by COD averaged 20 percent. The apparent mechanism of improved removal was the stimulation of greater biomass growth. PAC addition increased the oxygen uptake rate (OUR), the observed cell yield coefficient (Ybbs) and the first order substrate removal coefficient (Kb) of the activated sludge system, which were operated at a temperature of 18°C and a biological solids retention times of fourteen days. The addition of PAC also improved the sludge settleability but this resulted in higher effluent suspended solids concentration because zone settling Velocity was the primary factor affecting effluent suspended solids. A type of activated sludge bulking, known as jelly formation, plagued the biological reactors but nitrogen addition appeared to solve the problem / Master of Science / incomplete_metadata

Call number: LD2668 .T4 1985 L56 / Master of Science

During this thesis we tried to design, synthesise and analyse some novel devices for the selective delivery of peptides. These systems are based on the enzyme-activated anticancer prodrugs developed by Prof. Gesson in Poitiers and the peptide rotaxanes developed by Prof. Leigh in Edinburgh. The innovative rotaxanes we constructed are devised to protect and selectively release a peptide in response to an enzyme-specific stimulus for the targeted therapy of cancer. In Chapter 1 we tried to expose the main synthetic strategies aimed at improving the stability and permeation features of biologically active peptides. We examined some prodrug approaches and particularly the tumour-activated prodrugs (TAPs), largely investigated for use in anticancer chemotherapy. TAPs are generally three-part molecules composed of trigger, spacer and effector units. We also presented the original methodology developed by Prof. Leigh, namely the hydrogen bond-directed assembly of peptide rotaxanes, to protect a peptide thread from external environment. Finally we presented our project which consists of a combination of the peptide prodrug and rotaxane approaches. Therefore, based on the knowledge of both research groups we tried in Chapter 2 to develop some model systems in order to study the influence of the rotaxane architecture upon prodrug molecules. The first step towards such rotaxane-based peptide prodrugs relied on the efficient design of a spacer which has to be bulky enough to work as a stopper for the macrocycle. Much of the work presented in this chapter is based on the design and synthesis of such self-immolative units. We then explored the response of our model rotaxanes under the action of the activating enzyme. After this detailed study, in Chapter 3 we applied our concept to the biologically active peptide Met-enkephalin. In this chapter we presented a comparison between a rotaxane prodrug of Met-enkephalin and its non-interlocked derivative. Thus both compounds were successfully synthesised and evaluated to release the free peptide after enzymatic activation. The protective effect of encapsulating the peptide within a rotaxane assembly was also studied in human plasma and with different proteases. Finally, in Chapter 4, we introduced the construction of a rotaxane-based molecular machine programmed to synthesise a short peptide unit from the amino acids carried on its thread. We synthesised with success a one-station model rotaxane to study the catalyst effect of the macrocycle. Unfortunately this model machine proved not to work and current research is still ongoing to achieve such a synthetic device.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: In order to exploit lower grade and complex platinum group metal resources, cheaper and more efficient alternatives to the conventional mill-float-smelt-refine route are being sought. Leaching of platinum and palladium with cyanide has been proposed a number of times as a promising precious group metals (PGM) process option, and although platinum extractions are problematic, progress into the understanding of cyanide leaching of PGM containing ore and concentrate has been made. The platinum and palladium leaching will typically take place at elevated temperatures, which can range from 55°C on heaps to 180°C in autoclaves, with a better degree of leaching occurring with higher temperatures. Although this process for Pt and Pd extraction is a promising process option, research regarding the feasibility of the subsequent upgrading and recovery of the pregnant PGM leach solution, however, has been lacking. Since the carrier-phase extraction of gold using activated carbon offers significant advantages over other processes in terms of simplicity, the high pre-concentration factor, rapid phase separation, and relatively low capital and operating costs, activated carbon was deemed the most suitable sorbent for a Pt and Pd adsorption and stripping process. Very little is published on the adsorption of PGM cyanides onto activated carbon and when the effect of impurities such as base metals and thiocyanate together with a suitable elution method, are considered, no information could be found in the open literature. This study was launched and in general it was found that the activated carbon process does seem to be a viable process consideration for the upgrading of PGMs in a cyanide leach stream. Adsorption rates for dilute PGM solutions (0.15mg/L Pt, 0.38 mg/L Pd, 0.1 mg/L Au) in a stirred vessel indicated a high rate of adsorption within the first 60 minutes (giving more than 98% recovery of precious metals). A comparison of the Pt isotherm (25°C) to Au isotherms from literature indicated a similar loading capacity, while that of Pd was found to be significantly lower. In common with most diffusion controlled processes, an increase in the adsorption rate of platinum, palladium and gold cyanide with an increase in temperature was observed, while experiments with consecutive contacts of the PGM cyanide solution onto the activated carbon revealed that with an increase in temperature, the amount of PGMs that were adsorbed, decreased with each loading. In the absence of free cyanide and base metals, it was found that after 4 consecutive contacts, 99% of the total amount of platinum and palladium adsorbed at 25°C, compared to 85% of the platinum and 83% of the palladium at 50°C. No difference could be seen between the adsorption of gold cyanide at 25 and 50°C after 4 contacts. It has also been established that the detrimental effect of free cyanide on the adsorption of PGMs will increase as the temperature increases. The detrimental effect of the presence of Cu and Ni was found to depend on the amount of these base metals adsorbed, which in turn will depend on the cyanide concentration and the solution temperature. Adsorption of Pt and Pd has been found to be significantly more affected by temperature, cyanide and base metals than the adsorption of gold and needs to be carefully taken into consideration with the design of a PGM adsorption circuit to ensure sufficient Pt and Pd recovery. It is therefore highly likely that an activated carbon recovery process for Pt and Pd cyanide will not be as robust as the gold CIS (carbon-in-solution) process, which is considered to be one of its main advantages. The feasibility of eluting platinum and palladium cyanide complexes from activated carbon was investigated. It was found that platinum and palladium elute from activated carbon almost to completion in 4 to 5 bed volumes (BV) at 80°C, while the elution of gold at this temperature is slow, with a significant amount of gold (≈ 55 %) still to be eluted after 16 bed volumes. An increase in Pt and Pd elution kinetics was demonstrated with an increase in temperature with 99% recovery achieved at 4 BVs with an elution temperature of 95°C. Cyanide pre-treatment has been found to have a large influence on PGM elution. The effect of the NaCN concentration shows an increase in the recovery of Pt, Pd and Au as the cyanide increases from 0 to 2 %, after which the recovery starts decreasing again as the NaCN concentration increases from 2 to 4%. The NaOH concentration was also found to affect the PGM recovery and at 0% NaCN, an increase in the recovery is seen, while at a higher cyanide concentration (2 and 3% NaCN) a decrease in the PGM recovery occurs when the NaOH concentration is increased from 0.22% to 1.65%. A general decrease in Pt, Pd and Au recovery was seen as the ionic strength of the elution water increased and is consistent with literature on Au elution. The effect of a hydrochloric acid pre-treatment, which forms part of the process to remove calcium build-up from the activated carbon, was investigated, and for all the cases the Pt and Pd recovery increased when an acid pre-treatment was performed, compared to no acid pre-treatment. In none of the cases did any of the Pt, Pd or Au elute with the acid or the following rinsing water. The acid pre-treatment performed at 70°C removed a significant 64% to 75% of the Ni present and an additional 9.1% to 10.5% in the following rinsing water step. In the presence of copper cyanide, the elution order has been found to be copper, palladium, platinum and gold, which is the opposite order of adsorption preference. The cyanide pre-treatment has also been found to have a major influence on the elution of Cu and can be explained by the difference in the absorbance strength between the different copper cyanide complexes. The presence of Cu did not have a negative effect on the elution of the PGMs at strong pre-treatment (2% NaCN and 0.55% NaOH) conditions, but at weak pre-treatment conditions (0% NaCN) the recovery of Pt and Pd was reduced by between 10 and 18% after 5 BVs when Cu was present. The presence of 100 mg/L KSCN salt added to the leach solution during the adsorption stage, reduces the elution recovery of the PGMs at 4 BVs from 90% for Pt and Pd, when not present, to approximately 70% when present. The addition of the additional K+ ions reduced the recovery by less that 4% at 4 BV, which indicates that the possible formation of a PGM bonding with thiocyanate ([Pt(SCN)4]2- and [Pd(SCN)4]2-), which adsorb onto carbon, but doesn’t adsorb with water, cannot be ruled out completely. A maximum amount of 0.15% for Pt, 0.28% Pd and 0.6% Au was found to report to the pre-treatment solution at 25°C. For higher pre-treatment temperatures, the amount of Pt and Pd reporting to the pre-treatment solution increased significantly to approximately 8% at 80°C, while the increase in gold was marginal to 0.8% at 80°C. For the higher loading on the activated carbon (7000 mg/kg Pt and Pd), which is expected to be a better representation of plant conditions, 0.07% Pt, 0.11% Pd and 0.12% Au reported to the pre-treatment solution. The PGMs reporting to the pre-treatment solution is attributed to the distribution of the PGMs on the carbon particle, and even though very small, a certain amount of these PGMs would readily desorb or wash off the carbon. It has thus been established here that the stripping of adsorbed platinum cyanide complexes from activated carbon consists of a two step batch process, which involves the pre-treatment of the metal-loaded activated carbon with a relatively strong sodium cyanide and sodium hydroxide solution, prior to the elution step with de-ionized water at 80°C. Through the development of a mathematical model to describe this process, it was found that the rate of release of the platinum ions is governed by the amount of platinum and sodium on the activated carbon and the concentrations of these ions in the bulk of the liquid. This is mathematically described by a modified Freundlich isotherm equation and the mass transfer diffusion equation. The dependency of the platinum elution rate on the sodium concentration on the activated carbon, as suggested by gold related literature (Van Der Merwe and Van Deventer, 1990, Stange, 1990), is confirmed. Furthermore it has been found that the rate of platinum elution interchangeably depends on the equilibrium of the Pt ions at the carbon-liquid interface and the mass transfer of these Pt ions from the interface to the bulk liquid. As both of these rate-limiting factors were found to depend on the sodium concentration, the dominant platinum elution rate limiting factor shifts as the sodium concentrations change as the elution progresses. Four main time periods are used to simplify and to describe this process. The benefits of fundamentally understanding this process can ultimately lead to improved elution, better process control, shorter elution times, smaller elution columns or assist in the development of a continuous elution process. / AFRIKAANSE OPSOMMING: Nuwe prosesse om komplekse laer graad waardevolle metaal ertse te onwikkel in plaas van die konventionele maal-flotasie-smelt-raffineer proses word tans ondersoek. Loging van platinum en palladium met sianied is verskeie kere al voorgestel as n belowende proses opsie en alhoewel die ekstraksie van platinum nog 'n probleem is, is vordering al gemaak om die logings proses beter te verstaan. Die loging van platinum en palladium met sianied sal tipies plaasvind by hoër temperature wat kan wissel van 55°C in n hoop logins proses tot 180°C onder druk. Beter loging vind plaas soos wat die temperatuur styg. Alhoewel hierdie proses belowend is, is daar nog geen navorsing beskikbaar t.o.v die volgende stap in die proses wat die opgradering van die logings oplossing behels. Aangesien die gebruik van geaktiveerde koolstof in die goud industrie baie voordele inhou soos die eenvoudigheid van die proses, hoë opgraderings faktor, relatiewe vinnige adsorpsie en lae kapitaal en operationele kostes, mag hierdie tegnologie ook geskik wees vir Pt en Pd. Baie min is gepubliseer oor die adsorpsie van waardevolle metale (PGMs) met geaktiveerde koolstof en wanneer die effek van onsuiwerhede soos basis metale en thiosianied saam met n afstropings metode in ag geneem word, kon geen informasie in the literatuur gvind word nie. Hierdie studie is dus geloots en in die algemeen is daar bevind dat die geaktiveerde koolstof metode wel n geskikte oplossing bied vir die opgradering van PGMs in 'n sianied logings stroom. Adsorpsie snelheid vir verdunde PGM oplossings (0.15mg/L Pt, 0.38 mg/L Pd, 0.1 mg/L Au) in bekers wat geroer is, was vinnig vir die eerste 60 minutte (98% herwinning van die PGMs) en 'n vergelyking tussen die Pt adsorpsie isoterm en gepubliseerde Au isoterms wys op n relatiewe soorgelyke ladings kapasiteit. Die isotherm van Pd was egter laer. Soortgelyk aan meeste diffusie beheerde prosesse, het 'n verhoging van temperatuur gelei tot vinniger adsorpsie snelhede vir Pt, Pd en Au. Indien oplossings egter herhaaldelik met dieselfde koolstof in kontak gebring word, is bevind dat met 'n verhoging in temperatuur, die totale hoeveelheid PGMs wat absorbeer, met elke kontak verminder. In die afwesigheid van sianied en enige basis metale, het die totale hoeveelheid Pt en Pd wat geabsobeer is na 4 opeenvolgende kontake verminder van 99% by 25°C tot 85% adsorpsie van Pt en 83% Pd by 50°C. Daar was geen veskil tussen die adsorpsie van Au by 25°C en 50°C na 4 kontakte nie. Dit is ook vasgestel dat die negatiewe effek van vrye sianied in die oplossing, groter word soos wat die temperatuur verhoog. Die negatiewe effek van die teenwoordigheid van Cu en Ni, hang af van die hoeveelheid van hierdie metale wat absorbeer word wat weer bepaal word deur die sianied konsentrasie asook die temperatuur van die oplossing. Die mate waar in Pt en Pd ge-absorbeer word deur koolstof, word aansienlik meer beïnvloed deur temperatuur, sianied konsentrasie en die teenwoordigheid van basis metale as wat die adsorpsie van Au beïnvloed word. Met die ontwerp van n PGM adsorpsie proses, sal dit sterk in aanmerking geneem moet word, om seker te maak dat so min as moontlik Pt en Pd verlore gaan. Dit wys ook dat 'n geaktiveerde koolstof proses vir Pt en Pd, nie so onvatbaar vir proses veranderings sal wees soos wat die Au proses is nie, wat as een van die groot voordele van die Au proses beskou word. Die afstropery van die Pt en Pd sianied komplekse is ondersoek en gevind dat by 80°C, amper al die Pt en Pd binne 4 to 5 bed volumes (BV) van die geaktiveerde koolstof gestroop kan word. Die afstropery van Au by hierdie temperatuur is stadig en sowat 55% van die Au bly nog oor op die koolstof na 16 BVs. Die snelheid waarteen die Pt en Pd afgestroop word verhoog indien die temperatuur verhoog word en by 95°C is 99% van die Pt en Pd herwin na 4 BVs. Voorafbehandeling van die gelaaide koolstof met sianied, het 'n groot uitwerking op die PGM afstroping. Soos wat die NaCN konsentrasie verhoog word vanaf 0 tot by 2%, verhoog die PGM herwinning maar daal ook weer indien die NaCN konsentrasie verder verhoog word vanaf 2% tot by 4%. Die NaOH konsentrasie het ook n invloed gehad. By 0% NaCN, het die PGM herwinning verhoog soos wat die NaOH konsentrasie verhoog is maar by hoër sianied konsentrasies van 2 en 3%, is n daling in die herwinning waargeneem soos wat die NaOH verhoog is vanaf 0.22% tot by 1.65%. N algemene daling in die Pt, Pd and Au herwinning is waargeneem soos wat die ioniese sterkte van die stropings water toegeneem het. Dit stem ooreen met gepubliseerde navorsing oor die afstroping van Au. Om kalsium van die geaktiveerde koolstof te verwyder, word die koolstof vooraf met soutsuur gewas. Hierdie stap is vir Pt en Pd ondersoek en daar is bevind dat vir al die gevalle, die herwinning hoër was wanneer die gelaaide koolstof met soutsuur behandel is teenoor geen behandeling nie. In geen van die gevalle, is Pt, Pd of Au saam met die soutsuur of die daaropvolgende was water afgestroop nie. Voorafbehandeling met soutsuur teen 70°C lei wel daartoe dat tussen 64 en 75% Ni afgestroop word saam met die soutsuur en n verdere 9.1 to 10.5% saam met die daaropvolgende was water. In die teenwoordigheid van koper sianied, word Cu eerste afgestroop met Pd, Pt en dan Au wat daarop volg. Dit is presies die teenoorgestelde orde waarin die metale geabsorbeer word. Die voorafbehandeling met sianied, het ook 'n beduidende effek op die stroping van Cu. Dit kan verduidelik kan word aan die hand van die verskillende koper sianied komplekse wat vorm wat elkeen 'n verskillende affiniteit het vir adsorpsie. Wanneer 2% NaCN en 0.6% NaOH in die vooraf behandeling stap gebruik word, het die teenwoordigheid van koper geen negatiewe invloed op die afstroping van die PGMs gehad nie maar die herwinning is wel met 10% en 18% verlaag by 5 BVs wanneer geen sianied in die voorafbehandeling stap gebruik is nie. Wanneer 100 mg/L KSCN sout by die adsorpsie stap gevoeg word, daal die herwinning van die PGMs in die stropings stap van 90% tot 70% by 4 BVs. Die addisionel K+ katione verminder die herwinning met slegs 4% by 4 BVs wat beteken dat die vorming van adisionele komplekse soos [Pt(SCN)4]2- en [Pd(SCN)4]2-, wat nie op die normale metode afgestroop kan word, 'n moontlikheid mag wees. N maksimum van 0.15% vir Pt, 0.28% Pd en 0.6% Au word in die vooraf behandelings stap af gestroop. Indien die temperatuur van hierdie stap verhoog word na 80°C, verhoog die hoeveelheid Pt en Pd wat na hierdie stroom raporteer na 'n beduidende 8% tewyl Au basies onveranderd bly by 0.8%. Vir geaktiveerde koolstof wat hoër gelaai is (7000 mg/Kg Pt en Pd) en dus 'n beter verteenwoordiging van aanleg kondisies is, het 0.07% Pt, 0.11% Pd en 0.12% Au raporteer na die vooraf behandelings stap. Dit word toegeskryf aan die verspreiding van die PGMs op die koolstof wat hoofsaaklik op die oppervlakte voorkom en alhoewel die hoeveelheid klein is, word 'n sekere hoeveelheid slegs afgewas. Dit is dus vasgestel hier, dat die afstroping van Pt 'n twee stap proses is. Die eerste stap is die voorabehandeling van die koolstof met 'n sianied oplossing en daarna volg die afstroping van die Pt met suiwer water teen ongeveer 80°C. Met die ontwikkeling van n wiskundige model, is bevind dat die snelheid waarteen die Pt afgestroop word, beïnvloed word deur die hoeveelheid Pt en Na wat op die koolstof oppervlakte is, asook die konsentrasies van die metale in die vloeistof. Dit word wiskundig beskryf deur n gemodifiseerde Freundlich isotherm vergelyking asook deur die massa diffusie vergelyking. Die Pt afstropings snelheid wat afhanklik is van die Na konsentrasie kan vergelyk word met die afstroping snelheid van Au wat ook afhanklik is van die Na konsentrasie (Van Der Merwe and Van Deventer, 1990, Stange, 1990). Verder is bevind dat die snelheid van Pt stroping afhanklik is van beide die ewewig van Pt ione by die koolstof-vloeistof grens asook die massa beweging van Pt ione van die koolstof-vloeistof grens na die vloeistof. Beide hierdie snelheids bepalende faktore word bepaal deur die Na konsentrasie en skuif soos wat die Na konsentrasie verander soos wat die afstroping plaasvind. Vier hoof tyd periodes word gebruik om hierdie verskynsel te verduidelik. Deur die proses fundamenteel te verstaan, kan uiteindelik lei tot 'n beter proses, beter beheer, korter afstropings tye, kleiner toerusting of die ontwikkeling van 'n kontinue proses.